166 DAVEM'OKT ACADEMY OF NATURAL SCIENCES. 



traces exist in place in our immediate neighborhood. Yet they are 

 found as outliers extending within a short distance from Le Claire, 

 furnishing, in places, seams of coal that have been workable. We 

 find similar outliers at Buffalo, from which coal has been brought in- 

 to our city. Thes^ separated Coal Measures are but the extension of 

 the Illinois beds; and all of them the deposits of an ancient sea. And 

 in passing, I suggest whether they may not be represented by what 

 has been called the "Carboniferous drift," from which Prof. Pratt 

 has collected some fine fossils, and in reference to which he has pre- 

 pared a paper for the x\cademy (see page 106). 



I come now to an interesting question: By what process does a 

 plant of the Coal Measures, of large size and delicate structure, find 

 its way down through the whole thickness of the shales and lime- 

 stones of the Hamilton; the twenty feet of solid limestone, the repos- 

 itorium of all Corniferous fossils so far found; and still lower through 

 twenty feet further of the Tion-fossiliferous rock below; or in other 

 words, how is it transferred from <7, to 5 ? This is the problem 

 to be solved. 



The researches of Prof. Hall will materially aid us in comprehend- 

 ing something of its nature. In his Cxeology of Iowa, he has given 

 several diagrams to show that the huge cavities so often found in the 

 Hamilton and the Helderberg, are found filled with the blue shale of 

 the Coal Measures. One of the most remarkable instancesof the kind 

 occurs in the face of the quarry between Rock Island and Moline. 



We are presented with what was once an immense cavity in the 

 rock, connected by a long neck or tube extending through to the 

 earth which overlies it, becoming thus the medium of communication 

 with the Coal Measures. It is filled with a deposit of clay entirely 

 different from anything in the Hamilton, and, moreover, contained 

 the cast of a shell distinct from any known in the surrounding rock, 

 very similar to a carboniferous form. This same clay, I have shown 

 in a previous paper read before the Academy, is found in Cook's 

 ({uairy; and this same clay is that from which our plant was exhumed. 

 If no other theory presented itself, we might be necessitated to re- 

 sort to this to account for the occurrence of the clay iti the quarry 

 we are considering. I suggest such slight modiKcation as will adapt 

 it to the case in hand. 



What are the ordinary phenomena that now meet the eye as we 

 look fromlikiff to bluff across the river? Is it not the entire disap- 

 pearance of all the rocks that once filled up the whole area''' The 



