GE^OLOGY OF I^A SAIvIvE) COUNTY. 23 



Ottawa. At Troy Grove, formerly Homer, are found 

 Lituitesundatus,Gonioceras anceps, Ormoceros bacekii, 

 Orthoceros fusiforme, Kndoceras Annulatum, E. proti- 

 forme,Petaria corniculum,Cteiiodoiita, Leptena sericea, 

 Strophomena alternata, Asaphus canalis, a trilobite, 

 Pentamerus, line, etc. 



The Trenton west of Ottawa and on Covell creek 

 contains many silicious nodules and irregular masses, 

 some of them a tine chert, which are undoubtedly the 

 remains of spong-es, many species of which have been 

 identified and published by Dr. E. Everett. 



Corals; Haly sites, two species; Pavistella stellata 

 and a few ofood specimens of Archimedes reversa — 

 screw coral found by A. C. Baldwin, of Deer Park, 

 are all which have been identified. The absence of 

 fossils in the St. Peters and their imperfect condition 

 in the calciferous have been noted. We venture, how- 

 ever, to name as certain Conocephalus minutus the tail 

 shield, a trilobite; Ophileta levata, Murchisonia, Ivin- 

 g-ula, from the calciferous. 



Lying- on the Trenton, where it is presect, 

 in places where it is wanting-, on the sandstone, 

 we find the rocks of the carbonic ag-e — the coal 

 measures, a vast collection of sandstones, lime- 

 sstone, shales, clays and beds of coal. In La Salle 

 county this formation is about fifty feet thick at 

 Marseilles, tw^enty-five to thirty feet just northeast of 

 Ottawa, is wanting- about Utica, over 600 feet thick at 

 La Salle and 211 at Streator, while in the central part 

 of the State its thickness exceeds 1,000 feet. 



On the eastern side of the county we have in the 

 Illinois at Crotty or Seneca shales or clays about fifty 

 feet thick; coal, two feet; fire clay, four to ten feet. 

 At Marseilles the bluff shows a heavy bed of sand- 

 stone some fifteen feet thick, and below this traces of 



