USA > Iowa > Decatur County > History of Decatur County, Iowa, and its people, Volume I > Part 23
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Group.
System.
Series.
Stage.
Sub-Stage.
Recent.
Alluvium.
Cenozoic.
Pleistocene.
Glacial.
Kansan
Drift.
Pre-Kansan ( ?).
Drift (?).
Westerville ( ?).
De Kalb.
Paleozoic.
Carboniferous.
Missourian.
Bethany.
Winterset.
Earlham.
Fragmental.
Des Moines.
Pleasanton.
CARBONIFEROUS
The Carboniferous of the Mississippi Valley is divided into two major divisions long known respectively as the upper and lower. The latter does not occur within the county and its only importance in this connection arises from the fact that the St. Louis limestone, one of its members, forms the floor upon which the coal measures rest. In any future deep drilling for coal the St. Louis will indicate the horizon below which it is inadvisable to prospect.
Loess.
Gumbo.
237
HISTORY OF DECATUR COUNTY
The upper Carboniferous is commonly known as the coal meas- ures, and the term Pennsylvanian series has been proposed to cover the same beds. In this immediate region it consists of two major members, known as the Des Moines and the Missourian, each divisible into subordinate groups. These correspond respectively to the lower or productive and to the upper or unproductive coal measures. Keyes has proposed 15 to consider each of these divisions as independent series; dividing the Carboniferous of the interior into the Mississip- pian, Des Moines, Missourian, and Oklahoman. While it is not cer- tain that these different divisions are of strictly equivalent rank, and probably some include more than others, it is a great convenience in discussion and in mapping to use the terms in the sense proposed, and for these reasons they are adopted here, leaving to future critical paleontologic studies the adjudication of the rank of the divisions.
DES MOINES SERIES
PLEASANTON SHALES
The Des Moines formation is but sparingly exposed within Decatur County. The best exposures are on Weldon River. Imme- diately south of the state line (township 67 north, range 24 west, section 28), at the wagon bridge over the Weldon, a thin sandy lime- stone is exposed about four feet above the water. The rock carries Productus costatus, but seems to show no specimens of Chonetes mesoloba which is usually found in the Des Moines strata. In physical characteristics it very closely resembles a bed found at the corresponding horizon in Madison and adjoining counties and it is confidently referred to the Des Moines formation.
At the bridge in section 15 of Morgan Township there is an expos- ure showing twelve feet of blue sandy shale of Des Moines character and differing from anything found in the Missourian of the region. The basal portion of the Bethany outerops high in the hills on the west side of the river, and beds probably representing the Earlham horizon have been opened up in a small quarry. In the first ravine west of Little River (section 16, southeast southeast) a sandy lime- stone corresponding in character to that found on Weldon River, near the state line, outcrops. It is here fourteen inches thick, and, as usual, non-fossiliferous. About six inches above it are traces of a three-inch black shale, an unusual member of the section and per- haps only locally developed. The arenaceous limestone outcrops again
15 Am. Geol., Vol. XVIII, pp. 22-28. 1896.
238
HISTORY OF DECATUR COUNTY
about two miles west of Weldon River on Lick Branch (southwest of southeast, section 17, Morgan Township), at which point it has more of the shaly character.
Along Grand River there are few exposures of the Des Moines, the fragmental limestone of the Bethany, or the Earlham, outcrop- ping usually at the edge of the flood plain. Near Davis City, how- ever, the upper portion of the lower beds may be seen. Along the small ravine leading down past the old lime kilns north of town (northwest of southeast, section 35, Burrell Township) below the base of the Bethany is the following exposure:
FEET
5. Shale 3
4. Shale, black, "slate". 1
3. Shale, drab, sandy 4
Farther down and near the mouth of the ravine is the following:
2. Shale, sandy, yellow. 6
On the main stream near the mill, and accordingly below the above, the following beds are exposed :
1. Shale, drab, clavey, with several thin bands of blue- black non-fossiliferous limestone. 4
It is stated that before the dam was put in, limestone used to show in the bottom of the river below these beds, and it is known to extend below the bottom land as far across the valley as the trestle opposite town extends. Limestone has also been encountered in wells north of Davis City under the low platform reaching out from the hills to the west and under the bottom land (northwest of southwest, section 7, and northwest of northwest, section 12, New Buda Township). Since the fragmental limestone is exposed on Diekenson Creek at a level above this bottom land (southwest, section 3) this lower lime- stone would correspond to the arenaceous limestone exposed on Wel- don River. No. 1 of the section as given would correspond to the same number in White's section 16 at this point. The other numbers give details of the beds comprised under No. 2 in his section. He mentions finding here specimens of Beyriehia americana, which he also collected
16 Geol. Iowa, Vol. I, pp. 321-322. 1870.
239
HISTORY OF DECATUR COUNTY
from corresponding beds in Guthrie County. This would strengthen the reference of the beds to the Des Moines.
The beds here referred to the Des Moines form the top of that formation. With the exception of the arenaceous limestone already mentioned they are predominantly shales. They are usually arena- ceous to a noticeable degree. They correspond in general facies and in stratigraphieal position to the Pleasanton shales of Kansas.17 While the actual equivalent has not been proven, it has been suggested 15 and it seems quite likely to prove the correct correlation. In the interests of simplicity of nomenclature the name applied by the Kansan geol- ogists may be used for these beds. They are not extensively exposed in Iowa, though they have been described in Guthrie,19 Dallas 2" and Madison 21 counties, and are known at other points. It is, perhaps, significant that to the east of the Bethany limestone one finds in Wayne, Lucas and Clarke counties a broad, open prairie, such as would readily be formed over the area of outerop of these shales by step and platform erosion.22 The actual surface is, of course, due to the drift, and the underlying step and platform is correspondingly obscured. The topography, nevertheless, serves to outline the prob- able outerop of these beds and would suggest that they are of greater importance than knowledge derived from their outerops alone would indicate. Their probable thickness and the character of the underly- ing beds is discussed in connection with the subject of coal.
MISSOURIAN SERIES
As will be seen by the maps, the major portion of the county is underlain by the Missourian, or upper coal measures. This forma- tion, as here developed, consists of several beds of limestone separated by shales of various types. This assemblage of shales and limestones taken together constitutes the Bethany limestone, the lowermost of the several subdivisions of the Missourian. The Missourian as a whole has not yet been much studied, though the Bethany limestone and its equivalents have received considerable attention in Kansas, Missouri and Iowa.
17 Haworth: Kansas Univ. Quart., Vol. II, p. 274. 1895; Univ. Geol. Surv. Kansas, Vol. I, pp. 154-155. 1896.
18 Keyes: Proc. Iowa Acad. Sci., Vol. IV, pp. 22-25. 1897.
19 Bain: Iowa Geol. Surv .. Vol. VII, 443-444. 1897.
20 Leonard: Ibid., Vol. VIII, pp. 78-82.
21 Tilton and Bain: Ibid., Vol. VII, 504-509. 1897.
22 Marbut: Mo. Geol. Surv., Vol. X, p. 29. 1896.
240
HISTORY OF DECATUR COUNTY
BETHANY LIMESTONE
At Bethany, Mo., where the limestone was first studied by Broad- head,23 the beds as now exposed yield the following sequence as shown along a small tributary of Big Creek running through the town. The first exposure, which shows the top of the Bethany, is near the railway bridge north of the depot, the top of the limestone being at about 888 A. T.
FEET
6. Limestone, fragmental, loosely cemented, with many specimens of Meekella striato-costata, Chonetes verneuilanus, Productus costatus, Athyris sub- tilita, Productus longispinus, Spirifer cameratus and Dielasma bovidens. 6
5. Shale, clayey, green to drab, with thin bands of lime- stone 2
4. Shale, clayey, drab to black. 2
3. Limestone, dark blue, two ledges, 9 and 3 inches thick respectively
1
2. Shale, black
1
1. Shale, black to drab, with irregular nodular and thin layers of impure black limestone, carrying large, well-formed Productus cora, Productus nebrascen- sis, Athyris subtilita, Myalina subquadrata (?), Schizodus sp? In the shale itself are Myalina sub- quadrata, Productus nebrascensis, Athyris sub- tilita, Rhombopora lepidendroides and plates of Eupachycrinus verrucosus 6
Below this exposure for some distance there are no outcrops, but in the western part of town there are some small quarries which show the following beds :
7. Shale, clayey, drab.
FEET INCHES 6
6. Shale, calcareous, transition beds, with Spirifer cameratus, Meekella striato-, costata, Productus cora, Productus cos-
23 Trans .- St. Louis Acad. Sci., Vol. II, 311, 1862; Mo. Gcol. Surv., "Iron Ore and Coal Fields," pt. ii, p. 77 et seq. 1873.
241
HISTORY OF DECATUR COUNTY
FEET INCHES
tatus, Productus nebrascensis, Rhombop- ora lepidodendroides, Fistulipora noduli- fera, Myalina subquadrata, Athyris sub- tilita, Derbya crassa.
5. Limestone, heavy ledge, many Fusulina sylindrica
4. Limestone, thin bedded, with many of the fossils collected above, particularly Athyris subtilita, Productus cora, Pro- ductus costatus, Spirifer cameratus and Meekella striato-costata
2. Unexposed
1. Limestone, thin bedded, with Productus costatus, Productus cora, Productus longispinus, Athyris subtilita, Spirifer lineatus, Spirifer cameratus, Spiriferina kentuckensis, Chonetes verneuilanus, Hustedia mormoni, Dielasma bovidens and Fusulina cylindrica 12-15
Not far from here is the mouth of the stream which enters just above the falls of Big Creek. The rock forming the falls lies prob- ably six to eight feet below the base of the limestone just described. It is about twenty feet thick, the upper eighteen feet being made up of a coarse but finely cemented limestone breccia, such as is shown in Fig. 2, Plate xxi. It is marked by long dark streaks which suggest corals, but which fail to show structure. The only fossil collected from it was Productus cora. Below the breccia is about two feet of fine-grained gray limestone, carrying large, well-formed Spirifer cameratus with Productus cora. The brecciated character of the lime- stone and the absence of marked sedimentation planes has yielded, under water action, rounded forms and knob and pot hole surfaces. (See Plate xxii.)
The general sequence found here with the four bodies of limestone. separated by shales, is the same as has already been found in central Iowa. The exposures in the latter region were first studied by White 24 and have been more recently reviewed by the present sur-
24 First and Second Ann. Repts. State Geol., pp. 71-72. Des Moines, 1868. Geol. Iowa, Vol. I, pp. 245-250. Des Moines, 1870.
Vol. I -16
1 6
2 10
10 8
242
HISTORY OF DECATUR COUNTY
vey.23 In many of the minute details even there is a close correspond- ence between the Bethany section and that of Madison and adjacent counties. The latter may be summarized as follows :
FEET
8. Limestone, thick and thin bedded, characterized by a particular abundance of Fusulina cylin- drica, and hence called the Fusulina limestone .. 15-30
7. Shales, predominantly dark colored and argilla- ceous, containing several thin bands of bitumi- nous limestone, which are usually quite fossilif- erous. About midway of the shales is a horizon which is particularly fossiliferous. The more usual forms, including Athyris, Productus and Spirifer, occur in great abundance and perfec- tion. With these forms are vast numbers of Derbya crassa with Myalina subquadrata, Myalina kansasensis, Myalina swallowi, Avi- culpecten ocidentalis, Productus nebrascensis, etc. Not far above this horizon is usually a thin band of limestone literally made up of Chonetes verneuilanus. The whole thickness of the shale is . 10-20
6. Limestone, medium grained, thin to thick bedded quarry rock, with Athyris subtilita, Productus cora and Meekella striato-cosata. Best exposed near Winterset, and hence called the Winterset limestone 12-15
5. Shale, usually dark and including a black bitumi- nous horizon 8-12
4. Limestone, well shown near Earlham, and hence called the Earlham limestone. Carries an abun- dant fauna, which will be noted later. 20
3. Shale, with bituminous horizon, and at many points a thin, black limestone. 3-8
2. Shales, sandy, light colored, very variable thickness 2-16
1. Limestone, fragmental, made up of irregular bits of lime rock, filled in with calcareous clay. In places the rock can be picked to pieces with the
25 Proc. Iowa Acad. Sci., Vol. I. pl. iii, pp. 26-271, 893; Iowa Geol. Surv., Vol. III, p. 137, 1895; Ibid., Vol. VII, pp. 446-451, 1897.
243
HISTORY OF DECATUR COUNTY
FEET
fingers, elsewhere it hardens up into massive, thick-bedded layers. Along a small tributary of Deer Creek, in Guthrie County, it is quite fossiliferous, yielding Spirifer lineatus, Spirifer cameratus, Athyris subtilita, Hustedia mor- moni, Productus longispinus, Naticopsis alto- nensis, Lopophyllumn proliferum, Orthis pecosi, Bellerophon sp., Straparollus sp., Arch- æocidaris sp. 10-15
As the Earlham limestone is particularly well shown in Decatur County and presents there many analogies to the beds at the type locality, the following details regarding the latter may be quoted.26 The typical section is given below :
FEET INCHES
11. Bed of soft, yellowish, magnesian, earthy lime- stone, decomposing readily when exposed to weather 4
10. Limestone in three heavy ledges at west end of quarry 4
9. Buff shale with Chonetes verneuilanus 4
8. Limestone, like No. 4. 2
7. Ashen shale with very few fragments of brachi- opod shells 6
6. Earthy limestone, decomposing readily, vel- lowish, carrying large individuals of Athyris subtilita
3
5. Drab shale, with Produetus longispinus, P. costatus, erinoid stems and fragments of other fossils 6
4. Quarry limestone, in thin layers, irregularly bedded 8
3. Unexposed 20
2. Sandstone, in heavy layers. 7
1. Base of sandstone to ereek, unexposed . 17
At one point the quarrymen had worked down in the bottom of the quarry and exposed, below No. 4, drab and black shales to the
26 Geol. Madison County, Iowa Geol. Surv., Vol. VII, pp. 514-515. 1897.
244
HISTORY OF DECATUR COUNTY
depth of three feet, and below the shales a ledge of limestone six inches in thickness.
Distributed through the limestone beds No. 4 are the following:
Lophophyllum proliferum, McChesney.
Meekella striato-costata, Cox.
Productus punctatus, Martin.
P. costatus, Sowerby.
P. longispinus, Sowerby.
P. cora D'Orbigny-P. prattenianus of authors.
Athyris (Seminula) subtilitia, Hall.
Hustedia mormoni, Marcou.
Spirifer cameratus, Morton.
Spiriferina kentuckensis, Shum.
Allorisma subcuneatum, M. & H.
Stem segments and body plates of crinoids.
Various species of Bryozoa.
Chonetes verneuilanus N. & P. is somewhat common in No. 9, but is very rare in the other members of the section. Spirifer cameratus and Produetus longispinus are most abundant near the base of No. 4, while Productus costatus and Athyris subtilita are more common in the upper layers. All the species enumerated, however, with the exception of Allorisma subcuneatum, range through all the beds making up No. 4.
The best exposures of the Bethany limestone in Southern Iowa are found along Grand River and its tributaries. From the out- crops found here a complete section can be made from the Frag- mental limestone at the base up to and above beds which farther north have been called the Fusulina limestone, but which, from their excellent development in that vicinity, may now perhaps be best called the De Kalb limestone.
In Union County there is an important bed of limestone which, from the fact that it is well shown on Sand Creek near Westerville, may be called the Westerville limestone. It lies some little distance above the De Kalb horizon. In Jones Township of Union County (section 28 and farther south along the river) the beds are exposed, showing the following section :
5. Limestone, ash gray, fine grained, thin bedded, becoming almost shaly at the top, with Productus cora, Productus eostatus, Spirifer cameratus, Athyris subtilita, Chonetes verneuilanus cf. gla-
245
HISTORY OF DECATUR COUNTY
FEET
bra, Lophophyllum proliferum, Straparollus subquadratus and Fenestelloid bryozoa. 10
4. Shale, gray, calcareous, with thin nodular bands of limestone 4
3. Shale, drab to black. 10
2. Limestone, impure, nodular, in two bands. 215
1. Shale, drab to black, well exposed at Westerville 8
These beds extend into Decatur County, being seen near Wester- ville, on Sand Creek, and on Grand River. It seems probable that the shale (No. 1) extends down to the top of the De Kalb or Fusulina limestone which is exposed near Grand River and was at one time quarried at the old Madarasz quarry. (Section 36, township 70 north, range 27 west.) The best exposures of the latter limestone, and the ones which may be taken as typical, are found a short dis- tance east of De Kalb station. (Section 28, township 70 north, range 26 west.) The section at this point is given below :
INCHES
5. Limestone, irregularly water worn 6
4. Shale, hard, drab. 6
3. Limestone, irregularly bedded. 8
2. Shale, calcareous, becoming in places a poor
grade of limerock. 2
1. Limestone, in thick to thin ledges. 48
The limestone is quite fossiliferous, the forms collected including Productus costatus, Productus longispinus, Athyris subtilita, Spirifer camerata, Spirifer kentuckensis, Dielasma bovidens, Derbya crassa, Lophophyllum proliferum and Fusulina cylindrica. This fauna is more abundant than is usually found in the same beds farther north, though no exhaustive collections have been made in Madison and adjoining counties, and many of the species collected at De Kalb are known to be present, sparingly at least, in the former regions. The marked predominance of Fusulina sylindrica which is so striking a characteristic of these beds in Madison County, is not so noticeable at De Kalb. This is probably due as much to the greater abundance at the latter point of the other forms mentioned as to any real decrease in the numbers of the Fusulina. It is, nevertheless, true that in the earlier advent, or at least culmination, of Fusulina the Decatur County
246
HISTORY OF DECATUR COUNTY
outerops show much closer relations to the rocks as developed at Bethany, than to the Winterset section. It is for this reason, in part, that the term, De Kalb limestone, is to be preferred to Fusulina lime- stone, since neither the presence nor the abundance of the latter form is found to be consonant with a constant stratigraphical horizon.
The beds below the De Kalb limestone are shown near the wagon bridge just north of the railway station. The section exposed is as follows:
FEET
5. Limestone, De Kalb, thin bedded, very fossiliferous 2
4. Shale, soft, gray. 2
3. Shale, fine black "slate" 1
2. Shale, black, soft 216
1. Shale, drab 4
These shales are not particularly fossiliferous, as the section does not extend down to the Myalina horizon already noted. The latter is well shown on Grand River at the bridge about three miles west of Decatur (township 69 north, range 26 west, section 30, southwest, southwest). The section at this point is as given below. Fig. 1, Plate xxiv.
5. Limestone (De Kalb) lower ledges only
FEET 3
4. Shales, drab to black, carrying Derbya crassa, Myallina subquadrata, Athyris subtilita, Pro- ductus nebrascensis, Lophophyllum lepiden- droides and plates of Eupachycrinus verrucosus, exposed as a slope. Thin ledges of limestone found on the slope made up of Chonetes verneu- ilanus 15
3. Limestone, blue to black, with Productus cora, Productus nebrascensis and Athyris subtilita .. 3
2. Shale, drab, clayey. 12
1. Limestone (Winterset), coarse bedded, with Athy- ris subtilita, Productus 'costatus and Meekella striata-costata 10
The Winterset limestone dips north here about five feet per hun- dred and its maximum thickness is not exposed. The dip seems to be local only. The Winterset is exposed south from the bridge as far as the abrupt turn of the river in the southeast corner of section 36,
247
HISTORY OF DECATUR COUNTY
Grand River Township. Within a mile the Earlham rock appears, and at the ford in section 7, of Burrell Township, the Fragmental rock is seen in the bed of the river.
The Winterset rock at the Decatur bridge is quite similar to the typical beds at Winterset, both in physical characteristics and the character and relative meagreness of its fauna.
The shales between the Winterset and the De Kalb limestone form one of the most marked stratigraphic horizons in the section, and their close resemblance in all particulars to the corresponding beds at both Winterset and Bethany will be at once seen. The same fossils occur and in the same perfection and abundance.
The shales below the Winterset and extending down to the Earl- ham limestone are not well shown on Grand River. Elsewhere they are usually about ten feet thick and carry about their middle a one- foot black slate horizon. The Earlham limestone is quite well shown near the bridge in northeast of northwest of section 5, Burrell Town- ship. The exposure, which is on the east side of the river just south of the bridge, shows the following beds:
FEET INCHES
6. Limestone, coarse grained, with Fusulina cylindrica and Athyris subtilita. . . 2
5. Shale, clayey, carrying Athyris subtilita and Chonetes verneuilanus 6
4. Limestone, quarry rock, 4 to 12-inch ledges, with Productus cora, Athyris subtilita, Hus- tedia mormoni, etc. 8
3. Shale, argillaceous, drab. 1
2. Shale, black "slate" 1
1. Shale, drab, soft. 4
6
The very strong resemblance of this section to the typical Earl- ham seetion as already given will be noticed at once. The partings in each case are of the same character and carry the same fossils. Hustedia mormoni, which is abundant wherever the Earlham is ex- posed, has not been collected from any of the higher beds along Grand River, although at Bethany it is found frequently at higher horizons.
The fragmental rock is not shown at the exposure just described though it is exposed a short distance below at water level. On Pot Hole branch, south of Terre Haute (township 68 north, range 26 west, section 29, southeast of northwest). it is present about ten
248
HISTORY OF DECATUR COUNTY
feet below the base of the Earlham, being firmly cemented and non- fossiliferous. A thickness of four feet is shown in the bed of the creek and more may be present. The Fragmental rock is also below the base of the quarries opened up southwest of Davis City (town- ship 67 north, range 26 west, section 3, southeast of southwest). Here it is also non-fossiliferous.
The exposures in and near Davis City show the Earlham beds excellently. They are the ones which have been much opened up, though the Winterset and the De Kalb are present high in the hills. From the Earlham limestone on Dickenson Creek, southwest of Davis City, the following forms were obtained: Productus longispinus, Productus costatus, Athyris subtilita, Spirifer cameratus, Chonetes verneuilanus, Fusulina cylindrica, Hustedia mormoni and plates of Archæocidaris and Zeocrinus.
In the eastern portion of the county, on Weldon and Little rivers, it is apparently the Earlham which is exposed, though the rock has not been opened up enough to make the determination sure. The Fragmental does not show, being concealed by talus and drift, but has been encountered in bridge excavations. A short distance south of Spring Valley, limestone, apparently the Earlham, is exposed along a small stream running into Little River from the east (south- east of southeast section 13). The stone is fine-grained, ash gray, breaks with irregular fracture and weathers white. One ledge as much as eighteen inches in thickness is indicated by the blocks found on the surface. The rock is said to be underlain by shales. The fossils found included Athyris subtilita, Productus longispinus, Productus costatus, Chonetes verneuilanus, and Spirifer cameratus.
Beds corresponding to those just described outcrop about a mile north (northwest of northeast section 13) along a tributary of Little River, and have been in fact opened up at several points in the vicinity. At the old Cole mill (northwest of northeast section 14) the section given below is exposed in the west bank of the river. The limestone is probably the Earlham.
FEET
4. Limestone, thick bedded, with Athyris subtilita, very abundant corals, and plates and spines of Archæocidaris 5
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