19 PALEONTOLOGY OF NEW-YORK. 



and up this river as far north as the Falls of St. Anthony in Minnesota, 

 In Wisconsin, Iowa, Illinois and Missouri, the same formations are reco- 

 gnizable, and everywhere marked by a few peculiar species. In Kentucky, 

 the same is true of these limestones ; and even in Tennessee, where the 

 great tenuity of all the older rocks causes an apparent mingling of several 

 formations, these divisions are still to be recognized. 



From the St. Mary's river on the north, to the Mississippi, I have 

 personally examined these beds at numerous points, as likewise in the 

 southern part of Wisconsin, in Iowa and Illinois ; and though the thick- 

 ness of each member is rarfely more than a few feet, I have never failed 

 to recognize more or less clearly the lithological characters by which each 

 is known in New- York, and likewise some of the more characteristic 

 fossils. When followed in a westerly or northwesterly direction, there 

 appears to be a gradual thinning out of these deposits, an increase of ar- 

 gillaceous matter, and an almost entire absence of the corals proper ; a 

 few of the Bryozoa still continuing. This fact is in harmony with the 

 conditions aflfecting the Chazy limestone, which thins out, as before stated, 

 somewhere in the vicinity of the Escanaba river, on the north of Lake 

 Michigan. 



The Trenton limestone proper, which gives character to the entire 

 period, is the most persistent of the different calcareous members. Large 

 accessions have been made to our knowledge of its extension and character 

 in other parts of the coimtry, since the publication of the first volume of 

 the New- York Palaeontology. The Geological Survey of Canada has shown 

 its wide extent upon the north and northwest, both in the Lower and 

 Upper Provinces. In its western extension, it shows, in like manner with 

 the limestones below, a gradual diminution in thickness, a larger proportion 

 of intercalated shaly lamina? and beds, and a decreasing number of fossils. 

 Nevertheless it maintains suflficiently its lithological aspect to be recognized 

 everywhere ; and even throughout the entire distance from the Hudson 

 to the Mississippi, it contains enough of its characteristic fossils to be 

 identified. It b well marked on the northern shores of Lake Huron and 



