The Maquoketa Shales. — James. 337 
west the arenaceous beds are lost and argillaceous and calcar- 
eous beds predominate. Beyond Lake Winnebago in Wiscon- 
sin, the calcareous shales have been recognized in several 
places and they were referred by Mr. Lapham to the "Blue 
limestone" group. Further Dr. Percival recognized the same 
shales as underlying the limestone of the "Mounds," and des- 
cribed them in his first report of the geological survey of Wis- 
consin." Professor Hall then goes on to say : 
"The first indication of the existence of this grouj) in Iowa was ob- 
served in some mound-like elevations near the Mississipi)i river, about 
eight or ten miles below Gutenberg. On examination these proved to 
be above the Galena limestone, and their summits capped by the 
Niagara limestone, with Pentamerus oblongus, corals, etc. The slope 
afforded no opportunity of obtaining a section of the beds between the 
two limestones ; but from the character of the soil, the gentle slope of 
the hill, and other indications, it was i)resumed that these beds occur 
here." 
"Our attention was subsequently directed by Mr. Childs to the site 
of an old mill on the Little Makoqueta, from which some fossils had 
been obtained, and which, from their previous examination, were in- 
ferred to belong to the Hudson River grouj). At this locality, though 
the shales were not seen in situ above water, it was evident that they 
had been thrown out in excavating the foundation of the dam ; and a 
slide of gravel and clay on one side of the stream may have covered 
up what was formerly an outcro]) of the same, since fragments are 
abundant at the margin of the stream. On another branch of the 
stream, upon the land of Mr. Pitts, there is an exposure of soft shales 
with calcareous bands containing abundance of Orthoceralites; while 
the shalj'' strata, in some j^arts, are filled with Tellinomya {Nucula) 
levata. The details of this section are given below : 
"17. Top of bank of stream; calcareous bed, compact comminuted 
shells ; a few Orthoceratites. 
16. Shale with graptolite-like markings 1 foot. 
15. Calcareous bed, with comminuted fossils 1 foot. 
14. Fissile shale 10 to 12 inches. 
13. More compact calcareous bed, with comminuted and minute fossils ; 
some Orthoceratites IS inches. 
12. Shaly calcareous bed, with comminuted and minute shells. l(i inches. 
11. Orthoceratite bed 8 or 10 inches. 
10. Shale (i inches. 
9. Orthoceratite layer 7 inches. 
<S. Shaly calcareous matter ; 6 inches. 
7. Orthoceratite bed 1 foot. 
0. Shale 7 inches. 
5. Calcareous bed, with Orthoceratites and minute shells. . ..8 inches. 
4. Shale with minute fragments of shells and graptolite-like mark- 
ings 10 inches. 
8. Concretionary layer 1 foot. 
2. Calcareous bed with minute shells like Orthoceratites 1 foot. 
1. Shale with Lingula, 12 feet from bed of stream 12 feet. 
This section is about twenty-five feet in thickness. The Orthocera- 
tites are noted as being extremely abundant. "The black shale at the 
base of the section," Professor Hall says, "is not unlike the Utica 
slate, and the presence of Lingula of a large and small species enhances 
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