Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay
Steven Dutch And Donn P. Quigley, Leaders
The main purpose of this field trip is to examine the Precambrian rocks ofthe Mountain area, where rocks of a great lithological variety are exposedin a reasonably compact area. The route to and from the field area has alsobeen selected to pass through a variety of interesting glacial landforms(Figure 1).
The field trip route heads west across the Fox River. Some shipping berthsare north of the bridge on the west side of the river, others are upriver(south). in 1979 the port of Green Bay was visited by 293 ships, of which260 were U.S. and Canadian lake freighters and 33 were ocean-going foreignflag ships. The port handled 2,800,000 tons of shipping. in the distance, is the Tower Drive Bridge, part of the I-43 system. Thebridge (made of Japanese steel!) spans the mouth of the Fox River at aheight great enough to clear the shipping channel. All other lower FoxRiver bridges are drawbridges. Waiting for trains and drawbridges is anintegral part of life in Green Bay.
The fact that the Fox River flows northeast into a narrow, elongate baysometimes poses environmental problems. When winds are strong from thenortheast, or when spring runoff flows into Green Bay while it still hasextensive ice cover, flooding may occur along the lower Fox River or theGreen Bay shoreline. Northeast winds can also pile ice along the bay shoreline and cause damage to homes near the water.
There will be several gentle rises and falls in elevation as we head westacross the city of Green Bay. Most of these steplike features are old shorelines which mark former high levels of Green Bay. The major recognizedshorelines are the Nipissing (600-605 feet), Algonquin (also about 605feet, but tilted), and higher stands at about 620 and 640 feet (Hough, 1976).The present bay elevation is 580 feet.
About 7 miles west of the center of Green Bay the route climbs through ahilly tract, formed by outwash terraces and some drumlins. The drumlinsform a series of parallel ridges. The route climbs onto an elevated plainwhich was mapped by Thwaites (1943) as an outwash plain overlain by Garylake beds. From here to about 2 miles north of Pulaski the terrain is mostlyflat with occasional undulating patches of ground moraine.
The first town directly on the route is Pulaski, whose center is dominatedby a large church and Franciscan Monastery. Northeastern Wisconsin isdotted with small ethnic settlements. Pulaski and nearby Krakow, of course,are of Polish origin. Many towns east of Green Bay were settled by Belgians. German and Scandinavian settlements are also common.North of Pulaski we begin to encounter hilly areas which are mostly outwashterraces. After passing the town of Gillett, some 19 miles beyond Pulaski,the landscape alternates regularly between hilly areas dominated by outwashterraces and flat lowlands which are mostly outwash and till plains. About7 miles farther north, near the town of Suring, some of the lowlands areglacial lake floors. Suring lies 10 miles north of Gillett.
Just west of Suring is one of the few true moraines on this portion of thetrip. A large gravel pit is being operated north of the road. The view atthe top of the moraine is interesting, with typical swell-and-swale topography. in the distance to the north are hills of resistant Precambriancrystalline rock in the field trip area.
From here north the route lies mostly in thick outwash. Several kettleponds lie on the route about 10 miles north of Suring. Shortly afterward,the first Precambrian outcrops appear, and the topography alternates betweenbedrock knobs and thick, sandy, pitted outwash.
Just north of the kettle ponds. Highway 64 joins from the right. About 4miles beyond, watch carefully for a large bedrock bluff on the right. Thisbluff, of Belongia Granite, is an excellent example of stoss-lee topography.The up-ice (north) side is smoothly streamlined while the down-ice (south)side is steep and blocky because of plucking. This bluff is not visibleuntil a few hundred feet away, so watch closely. From here to Mountain(1 1/2 miles) outcrops are numerous and highly varied in lithology.At Mountain we turn east onto County Highway W. This area was damaged bya tornado some years ago and fallen trees are still visible in the woodsjust east of town.
SE 1/4, NW 1/4, and NW 1/4, SW 1/4, Section 6, T31N, R17E, Oconto County,Wisconsin, Mountain 7.5-Minute Quadrangle.
This locality displays several Precambrian units within a short distance ofthe highway. in the woods about 100 m south of the highway are outcrops ofthe Waupee Volcanics. The rocks at this locality are thin-bedded meta-tuffsof the upper member of the Waupee Volcanics which strike ENE and dip steeplynorth. A few crenulations are visible.
Immediately north of the highway, the south side of the steep hill is madeup of Baldwin Conglomerate, a quartzose grit or small-pebble conglomerate.A few of the clasts are similar to the Waupee Volcanics south of the highway, and are generally believed to indicate that the rocks here are youngerto the north. Mancuso (1960) correlated this unit with the Thunder Mountain and McCaslin Quartzites and considered this area to lie on the southernlimb of the McCaslin Syncline.
Higher up the hill, the Hagar Feldspar Porphyry is exposed. Caution theHill can be very slippery in wet weather. This rock has a black groundmasswith large pink feldspar and blue-gray quartz phenocrysts. The term "Rhyolite" was originally applied by Mancuso to most of the fine-grained igneous rocks in this area, but most have been remapped as intrusive rocks. Hagar Rhyolite is presently mapped north of the feldspar porphyry. it is lighterin color but otherwise similar in texture.
NW 1/4, NW 1/4, Sec. 5, T31N, 417E, OcontoCounty, Wisconsin, Mountain 7.5-Mlnute Quadrangle.
Intrusive rocks associated with the Penokean orogeny (1600-1900 m.y.) arewidespread in central Wisconsin but rare in this region. A possible example of such a rock is the McAuley Granite Gneiss. The McAuley Gneiss is a homogeneous pink or gray granitic gneiss composed of quartz, K-spar, plagloclase and biotite. There is no banding. The follationchanges strike abruptly with no obvious pattern.
Two explanations for the contorted foliation have been advanced. One, the moreconventional, is that the foliation is due to Penokean deformation of a smallgranitic intrusive. In this view the McAuley probably intruded the WaupeeVolcanics and was then deformed later (or simultaneously) during the Penokean orogeny.
The other view, suggested by Read and Weis (1962), is that the McAuleyGneiss formed by metamorphism (granitization) of the tuffaceous member ofthe Waupee Volcanics, and that the irregular foliation is a relic of theoriginal bedding, which was disturbed by post-depositional slumping. insupport of this view, the McAuley Gneiss does lie along the strike of theWaupee Volcanics at Stop i, is about the same width as the upper tuffaceousand metasedimentary members, and is mapped as having a gradational contactby Medaris and others (1973, p. 53). The present author favors the moreconventional interpretation, above, however.
Several types of late dikes occur in the gneiss. Near the road is a foliated greenstone dike which displays marked differential weathering. Alsonear the road is an aplite dike which cuts and offsets a thick quartz vein.At first glance this looks like a clear case of faulting before or duringintrusion, but the geometry is also explained by simple dilation of thedike during intrusion (Figure 2). Several irregular masses of pink apliteoccur higher up the hill.
Figure 2. Offset dike in the McAuley Gneiss. A. offset dueto faulting, 6. offset due to dilation during intrusion.
Deformed Waupee Volcanics. NW 1/4, SW 1/4, Section 5,T31N, RISE, Oconto County, Wisconsin, Shay Lake 7.5 minute Quadrangle.
We turn south from Highway W onto the West Butler Rock Road. Butler Rockis a large knob about 5 miles south of Highway W. The route passes firstover a hilly area dominated by sand ridges (small eskers?), then across ashort marshy stretch (glacial lake floor), then into a hilly area of pittedoutwash. From the bus stop, proceed 0.4 miles down the jeep trail, then upa side track to the top of Butler Rock, about a 200-foot vertical ascent.This route is passable by field vehicle but not by bus! if the weather isfair and the foliage at its peak the view from the top should be spectacular. In the event of inclement weather this stop will be omitted becauseof the long walk it entails.
A detailed map of Butler Rock is presented in Figure 3. The overall geologyof Butler Rock consists of E-W striking, roughly vertical rocks of the Waupee Volcanics, but with great small-scale structural complexity. Boththinly-laminated and massive units are present, the former possible representing tuffs or volcaniclastic rocks, the latter flows or dikes. Shearzones are very common, as are irregular patches of epidotization.
3. Structural sketch map of Butler Rock.
At Substop A is a fairly convincing example of a ventifact. The epidotepatches are highly polished, and one contains a sharp-edged ridge veryreminiscent of those which occur on dreikanters. Considering the highlocation and the amount of sand at the base of the hill, wind abrasionseems fairly plausible, especially during the late Pleistocene when periglacial conditions prevailed.
At Substop B, a small dike about 1m thick has been complexly folded andsheared. The axial plane of the folding is about parallel to bedding andstrikes about 115 (Figure 4).
A small fold, one of the few which can be found on an outcrop scale in thisarea, occurs at Substop C. The fold is Z-shaped with an axial plane traceof 77. The core of one half of the fold has been crushed and sheared(Figure 5). The geometry of this fold is hard to reconcile with the geometry of the McCaslin Syncline. There does not seem to be any evidencefor a west-closing fold between here and the McCaslin Syncline, such asclassical structural geology would predict. it may be that this foldrepresents a. different deformation event than the one which formed theMcCaslin Syncline.
|Figure 4 |
Folded dike on ButlerRock (Substop B) Areashown is about 10 m across
|Figure 5. |
Z-fold on Butler Rock(Substop C) Area shownis about 5 m across.
Center of NW 1/4, Section 5, T32N, RISE,Marinette County, Wisconsin, Thunder Mountain 7.5-Mlnute Quadrangle.
Lunch Stop Water and rest: rooms available.
The first item of interest is a small knob in the middle of the south lawn.It consists of conglomerate sprinkled with attractive red euhedral garnets.No hammering, please. Read and Wels (1962) suggested this might be a slumpbreccia, but the texture could just as easily be that of a normal quartzitic conglomerate.
-31-The hill west of the hatchery buildings is made up of impure quartzite whichstrikes north-south and dips 40-50 W. A large sill of metadiorite occupiesmuch of the top of the hill. Both contacts are visible. The metadioritecontains some quartzite xenoliths.
This locality lies at the eastern end of the McCaslin Syncline, and theattitude of the rocks here is consistent with the overall picture of a west-plunging syncline. The quartzite is conventionally mapped as the southernend of the Thunder Mountain Quartzite, but it is quite different from themain mass of quartzite. The quartzite at this locality is fine-grained andthin-bedded, whereas the main body of the Thunder Mountain Quartzite ismassive, coarsely crystalline, and much purer. Thunder Mountain is visibleas the high hill to the northwest. The best outcrops on Thunder MountainItself are on the west side in an area accessible by 4-wheel drive vehicles,The more accessible east side is thickly mantled with glacial deposits andhas few outcrops. The map of Medaris and Anderson (1973) shows the rocksat this stop as being part of the Waupee Volcanics.
SE 1/4, NW 1/4, Section i, T32N, RISE, MarinetteCounty, Wisconsin. High Falls Reservoir 7.5-Mlnute Quadrangle.
Several intrusive rock types are visible at this stop, as well as a varietyof anomalous ice-flow indicators.
The igneous nomenclature at this stop has been quite confusing. The mainrock types are a pinkish rock with large rounded quartz phenocrysts and adark gray to black, medium-grained porphyry. Read and Wels (1962) calledthe pink rock Hagar Rhyollte and the dark unit Peshtigo River Porphyry.
Small granitic pods within the gray unit were called High Falls Granite.Medarls and others (1973a) correlated the pink unit with the Belongia Granitewhich occurs over a wide area south of Mountain, and called the dark unitPeshtigo Trachyandesite. The granitic veins and pods within the PeshtigoTrachyandesite were considered to be a syenitic border phase of the BelongiaGranite.
The Belongia Granite at this stop is an attractive, distinctive rock whichconsists of a fine-grained pink goundmass that encloses 5-mm rounded phenocrysts of translucent gray quartz and pinkish K-spar. The quartz phenocrystsare far more conspicuous than the K-Spar. The porphyritic texture probablyled to the early identification as rhyollte, but there are no signs of layering or flow banding, and an intrusive origin seems more likely.
The Peshtigo Trachyandesite is a dark, quartz-poor unit with small grayfeldspar phenocrysts. its relations with the Belongia Granite are gradational,but Medarls and others (1973) felt that it predates the Belongia granite.Both of these units are considered part of the Wolf River Bathollth, an anorogenic granitic complex which has been dated between 1450 and 1500 m.y. old.The arrangement of the Belongia Granite and Peshtigo Granite and PeshtigoTrachyandesite, as well as several other units, is arcuate , and Medaris andothers (1973b) suggested that this portion of the Wolf River Batholith maybe a ring complex. A number of ring complexes occur in central Wisconsin onthe western margin of the Wolf River Batholith.
Substop A (Figure 6) is a low rounded hill of Belongia Granite with incipientspheroidal weathering. Nearby, at B, is a small but perfect roche moutonee.Note that the ice flow, as indicated here, was from SE and NW. The same iceflow direction is indicated at C, where both chatter marks and very largecrescentic gouges occur.
Ice flow indicators around High Falls Reservoir all show an anomalous ice-flow direction from SE to NW (Figure 7). A possible explanation might bethat ice from the Green Bay Lobe to the east spilled into the Peshtigo RiverValley and spread both up and down-valley.
Figure 7. ice-flow indicators in the High Falls area. Data collected by TomBader and Dave Comb under the supervision of Ronald Stieglitz and Joseph Moran.Arrows show directions of flow as inferred from stoss-lee features, chatter marks and crescentic fractures. Unornamented lines indicate striations. Dot incenter of each symbol indicates location of data point.
The small peninsula D is made up mostly of Peshtigo Trachyandesite, withpatches of granitic or syenitic material which is considered a border phaseof the Belongia granite. A curious feature is the presence of deep groovesof roughly semicircular cross section. At the bottom of some of them is ajoint with a narrow band of alteration on either side. Evidently some combination of deep weathering and mechanical erosion is responsible for thesegrooves.
High Falls Dam was built in the 1920's to provide power for the city of GreenBay. it now is used only for local power needs.
From High Falls Dam to Crivitz the route passes through hilly terrainformed by pitted outwash and recessional moraines. South of Crivitz theterrain becomes gentler and is mostly ground moraine and thin outwash.Between Crivitz and Found is a historical marker which marks the halfwaypoint between the equator and the North Pole. The latitude is not 45, asone might expect, but 45 8' 45.7". The distance to both the equator andthe pole is 3107.47 miles. The discrepancy in the latitude is due to theway latitude is measured. Latitude is not defined by the angle between alocation and the equator, measured from the center of the earth. Rather,it is defined by the angle a line normal to the earth's surface makes withthe equatorial plane. Obviously, if you're going to measure positionastronomically, it makes more sense to refer to the local vertical ratherthan some oblique line passing through the earth's center. The slightlyellipsoidal shape of the earth causes degrees of latitude to be slightlyshorter at low latitudes than high (Figure 8).
Figure 8. Measurement of Latitude
Just north of Pound, about 10 miles south of Crivitz, the route passesbetween sand hills which are part of a large esker. The esker trendsroughly E-W and can be traced for about 10 miles. Most of the conspicuoussand hills for the next 10 miles or so are eskers.Near Stiles, about 20 miles south of Crivitz, the terrain flattens out intoa former floor of Green Bay (Thwaites, 1943). Much of the region betweenStiles and Green Bay was devastated by the Peshtigo fire of 1871 (seefollowing article). The few hills between Stiles and Green Bay are mostlysand dunes.
The region north of Green Bay was devastated by the worst forest firedisaster in North American historyon October 8. 1871, the same day asthe much more famous Chicago fire.The following account is largelyfrom Wells (1968).
After the depletion of the New Englandforests, lumbering activity in theU.S. shifted west to the Great Lakes.The original forest of northern Wisconsin was white pine, which furnished
lumber for the expanding settlementsof the Midwest. Settlers in thosedays were extremely careless withfires, which usually tended to burnthemselves out in the sparse understory of the then-virgin forests.In the warm, dry fall of 1876 therewere many small brush fires in northeastern Wisconsin. it had only rainedonce since July.
On the evening of October 8, 1876, theweather changed. Strong winds causedthe many small fires to coalesce intolarger fires. The main fire started just northeast of Green Bay and burned much of the lower Door Peninsula. Manypeople believe the fire "jumped" acrossGreen Bay, and in support of this idea,there are reports from ships in the bayof large burning branches falling faroffshore. it is more likely, however,that the fires east and west of the bayoriginated independently.
Figure 9. Area destroyed by forestfires, October 8, 1871.Open circles show townswhich were not destroyed,closed circles show townswhich were destroyed.
Some settlers, aware of the fire danger, had plowed firebreaks around theirhomes. These helped if the fire was not too intense, but: in many areas thefire developed into a true firestorm and killed people who were in the middleof large clearings. Even previously burned-over ground was not always asafe refuge.
A number of villages were destroyed, most notably Williamsonville, nearBrussels on the Door Peninsula, where 60 died. But by far the worst tollwas taken at Peshtigo. When the fire danger became acute, the citizens ofPeshtigo headed for the Peshtigo River, but many never made it. Of the 2500people then living in Peshtigo, 600 died. including many Scandinavianimmigrants who had arrived only a few days earlier. Some accounts say aslittle as ten minutes elapsed between the time the fire arrived at Peshtigoand the time the entire town was burning.
There are as many remarkable stories of the fire as there were people involved.One man. Reed Lovett, ran for a stream but was caught by the fire. Hedecided a quick death was preferable to a slow one, so he pulled out hisknife and stabbed himself in the chest repeatedly. Meanwhile he kept running,eventually falling into the. stream. He survived. The parish priest atPeshtigo, Father Pernin, put his altar vessels in a cart and headed for thePeshtigo River. Despite the fire. being so intense that some people died onlya few feet from safety in the river, the people in the river found theirclothes catching fire, the altar vessels were undamaged, an event which manyCatholic survivors, not surprisingly, considered miraculous. it finally rainedon October 9, the day after the fire.
After the fire, it was found that in some areas even the stumps and roots oftrees had been consumed. At least 1,150 people are known to have died. Thelast known survivor of the tire, Mrs. Augusta Wegner Bruce, who was two yearsold at the time, died in 1974 at the age of 104.
The governor of Wisconsin was out of the capitol directing relief efforts forvictims of the Chicago fire when word arrived on October 10 of the disasterat Peshtigo. His wife, Many Fairchild, though she lacked legal authority todo so, ordered relief supplies bound for Chicago to be diverted north toPeshtigo, an action which won her praise for her decisiveness.Geology played a role in saving two other cities from a similar fate.Marinette, Wisconsin and Menominee, Michigan are only seven miles north ofPeshtigo. Had the fire reached them with the same intensity, the disasterat Peshtigo would very likely have been repeated. However, north of Peshtigothere are many sand ridges, stabilized sand dunes formed during Pleistocenehigh stands of Lake Michigan. The vegetation is sparser on these ridges,and the fire was manageable when it reached Marinette and Menominee, so thatthese cities were largely spared.
There are few tangible traces of the fire today; little was left afterward.Perhaps the most poignant relic is in the Beyer Home Museum in Oconto: acharred dollar bill taken by his father from the pocket of a boy who died inthe fire. A small museum in Peshtigo contains a few items, notably a dimeand half dollar fused together by the heat. Next to the Peshtigo Museum isthe cemetery where 300 victims are buried in a common grave. A few of thevictims have individual grave markers, but these rarely mention the fire.Evidently the survivors felt that the date October 8, 1871 told the storyby itself.
There are virtually no clear geologic or physiographic signs of the fire.The fire occurred late enough in the fall that little erosion occurred beforethe winter snow cover, and erosion the following spring was probably minimalas the area became revegetated. The ash layer has been obliterated by weathering and plowing. Probably the most lasting effect of the fire was the rapid (!) clearing of a large part of the lower Door Peninsula which hastenedthe opening of that area to farming.
In the event that severe weather forces the cancellation of Stop 3 (ButlerRock), we will visit the following two stops as time permits. They illustrate some of the lower Paleozolc stratigraphy of northeastern Wisconsin.
SE 1/4, SE 1/2, Sec. 33, T31N, R19E, Coleman, 15-Minute Quadrangle.
One of the few Cambrian outcrops in northeastern Wisconsin is located northof Highway 64 about 5 miles west of Pound. The friable nature of the Cambrian sandstones, and the coincidence of the recessional moraine belt withthe Cambrian outcrop belt, combine to make outcrops very rare.
The sandstone exposed here is a fairly well-indurated, pure quartz sandstonewith thin (10 cm) beds. The beds form low outcrops in the stream bank and ledges in the stream. No fossils have been found yet at this particular locality.
SE 1/4, NE 1/4, Sec. 6, T28N, R21E, Oconto West 7.5 minuteQuadrangle, Wisconsin.
Contact between Platteville Dolomite and Saint Peter Sandstone (both Ordovician).
The low hill on which the quarry is situated is an outlier of PlattevilleDolomite. in the quarry it is massive or thick-bedded and buff in color,grading into thin-bedded, blue-gray shaly dolomite near the base. Fossilsare abundant: the massive dolomite contains abundant branching bryozoans,and the shaly material is rich in trilobite fragments. Recent reactivation of the quarry has exposed good trilobites, cephalopods, brachiopodss, andcrinoids. Several complete crinoids and long crinoid stems have been foundand are now in the UWGB study collection.
In the southern end of the quarry, the floor of the quarry is Saint PeterSandstone, noted for its purity and good sorting. Here it is somewhat iron-stained but in other parts of the Midwest it is pure enough to quarry forglassmaking. it is generally weakly cemented, and at this locality it isvery friable. The contact with the overlying Platteville Dolomite is somewhat gradatlonal over a meter or so.
This stop is labeled a Gravel Pit on the topographic map. Errors on U.S.G.S.maps are quite rare: the Survey tries to attain an accuracy of one error orless per 100,000 map symbols.
Created 25 July 2001, Last Update 13 January 2020
Not an Official UW-Green Bay site