114 Wisconsin Academy of Sciences, Arts, and Letters. 



I 



the Silurian age — usually termed the Lower Silurian, where by 

 successive layers or strata of calcareous or siliceous sedimentary 

 matter, we trace each order of life through distinctive periods, and 

 epochs, until progressive organization culminated in the era of 

 man. 



The nomenclature adopted by tacit consent of paleontologists, 

 to be applied to rocks, is that of the locality where the exposure of 

 a specified rock exists in its best state of preservation and can be 

 carefully examined and studied. 



In this manner are the terms derived, Canadian, Trenton, Nia- 

 gara, Salina, Lower and Upper Helderberg and Hamilton, with 

 the subdivisions of Quebec,- Galena, Waukesha, Eacine and St. 

 Claire. 



But it is the three principal periods: the Trenton, Niagara and 

 Salina which particularly interest a paleontologist when making 

 collections of paleozoic remains from the eastern portions of Wis- 

 consin, and therefore the foregoing explanatory observations 

 seemed to be necessary to elucidate what seemed to befog or dc' 

 ter some of our leading state geologists in arriving at definite sat- 

 isfactory conclusions. 



For if you examine the strata of rocks, with their fossiliferous 

 contents, as exhibited in various exposures by quarrying or from 

 other causes in Milwaukee county within a radius of twenty miles, 

 it is difficult to apply the foregoing mentioned, or geological ax- 

 ioms. In a single quarry containing a coralline limestone near 

 Wauwatosa I have obtained several thousand specimens within the 

 past twenty years, and from among them I can show you repre- 

 sentative fossils delineated and described as belons-inar to the com- 

 mencement of the primordial time or Lower Silurian age, intermin- 

 gled with many fossils characteristic of the Upper Silurian, the 

 Guelph and the beginning of the Devonian age. However, "Prof. 

 Dana asserts that there is no evidence that a species existed la 

 the latter half of the Upper Silurian, that was alive in the latter 

 half of the Lower Silurian." The fossils of the Niagara fauna 

 being mostly casts of the interior, it is more of an exception to 

 find the shell or testaceous covering in a perfect state of preser- 

 vation thereby making our investigations accompanied with many 



