274 Field Columbian Museum — Geology, Vol. II. 



Crinoids 21 specimens, 7 species; 



Brachiopods 96 specimens, 9 species; 



Trilobite 1 fragment. 



Of this material the corals, sponges and crinoids showed a great simi- 

 larity to those found at St. Paul, Indiana, and Perry county, Tennessee, 

 and a number of species described from those localities were recognized. 

 It was found that the manner of preservation of the clay pocket fossils 

 differed from that usual to those of the limestones of the Chicago 

 Area in that the latter are natural casts and molds .while the clay-pocket 

 fossils are silicified. Search in the surrounding limestone at Romeo 

 failed to show similarly preserved fossils in place there and only a few of 

 the clay-pocket species were discovered. The spoil heaps of the Chicago 

 Drainage Canal were then studied and near Lemont, Illinois, the species 

 found in the clay began to appear, until all the brachiopods and part 

 of the corals were found. Many of these were in a similar state of 

 preservation to those of the clay pockets. Of the seven species of 

 crinoids occurring in the clay three were found in the Lemont limestone 

 and three more were represented by species of the same genera. Over 

 400 fossils, representing 76 species, were collected at this locality, 

 divided as follows : 



Sponges 3 specimens, 1 species ; 



Corals 40 specimens, 6 species ; 



Cystoids *. 62 specimens, 6 species; 



Crinoids 149 specimens, 32 species; 



Bryozoans 10 specimens, 6 species; 



Brachiopods 62 specimens, 11 species; 



Mulluscs 9 specimens, 5 species; 



Trilobites 82 specimens, 9 species; 



The finding of these silicified corals and brachiopods at Lemont 

 identical with those occurring in the clay pockets, left little room for 

 doubt that the clay and fossils found in it were residual from the 

 Niagaran limestone, and that they had been transported to Romeo from 

 the Lemont Area. The Romeo quarry is distant about five miles in a 

 southwesterly direction from the point near Lemont where the cor- 

 responding fossils were found. Both localities are in the valley known 

 as the Chicago Outlet, through which the waters which occupied the 

 basin of Lake Michigan at the close of the glacial period discharged 

 into the Mississippi River. The flow of these waters would have been 

 sufficient to transport material like that described from Lemont to 

 Romeo, although the period and exact circumstances of this deposition 

 have not as yet been determined. The silt-like nature of the deposit 

 in the clay pockets shows that it occurred in quiet waters. 



