1 58 Prof. Rogers* s Address before the 



mote. In the above system we try to give to geological language the 

 capacity of expressing the facts and laws of gradations in strata which 



are so constantly appearing* 



As an illustration of the necessity for some such general applicable 

 scheme for our Palaeozoic rocks, it may be mentioned, that while some 

 of these are remarkable for adherence to their typical characters, others 

 are conspicuous for their protean variations. The value of our partic- 

 ular mode of designation, may be seen in the instance of the group of 

 formations we have called the Matinal series. Being remarkably well 

 separated by great natural features from the Primal series below, and 

 from the Levant series above, from both of which it is insulated as well 

 by clear mineral characters as by dissimilarity of organic remains, it 

 yet exhibits within itself, when widely traced, several important modifi- 

 cations of type, which no geographical or other artificial nomenclature 

 can possible indicate or express. Thus it consists in New York of five 

 rather well defined formations, the calciferous sandstone, black lime- 

 stone, Trenton limestone, Utica slate and Hudson river group, each 

 possessing an easily distinguishable mineral aspect, and its own organic 

 remains with little intermixture. But how different is the condition of 

 the whole mass in Ohio and Kentucky, and again how different in south- 

 western Virginia and East Tennessee. In the anticlinal district of Cin- 

 cinnati and Lexington, where the series bears the name of the blue 

 limestone, not one of the special subdivisions or formations, so easily 

 recognized on the Mohawk, can be distinguished, but the whole displays 

 a fusion or blending of the different portions, and also of the mineral 

 materials which baffles every attempt at tracing an exact equivalency 

 between any of the parts and the New York formations. It is true the 

 investigations of Prof. Locke, Dr. Owen and other geologists, show that 

 certain species observe certain horizons, but it should be observed that 

 these horizons in many cases, do not bear to each other the same rela- 

 tions which those of the same fossils do on the Mohawk. In place of 

 the five rather clearly marked masses o( New York, the whole expo 

 portion in Ohio, is about one thousand feet in thickness, composed o 

 attenuating calcareous shales and thin layers of limestone. 



Turning to Virginia and East Tennessee, we have a still different 

 state of things ; the Mohawk type, with no very important modifi- 

 cations, continues from New York through New Jersey, Pennsyl- 



sed 



vania, and Maryland, extending into Virginia as far as the north 

 branch of the Shenandoah, some seventy or eighty miles southwest of 

 the Potomac. The principal change in this distance is in the Black 



