MARYLAND GEOLOGICAL SURVEY . 31 



principles upon which the Ozarkian and Canadian have been founded are 

 discussed in great detail in the Eevision and their author has a mono- 

 graphic study on their paleontology and stratigraphy in the course of 

 preparation. Although each of the new systems (Ozarkian and Cana- 

 dian ) contains strata heretofore in the one case referred to the underlying 

 Cambrian and in the other to the overlying Ordovician, much the greater 

 part of each system is composed of thick formations whose actual dis- 

 tinctness from the typical Cambrian and Ordovician has never been 

 appreciated. In short these two systems, like the Cambrian, Ordovician 

 and all well-founded geologic systems, are based on a certain sequence of 

 diastrophic events and a sufficient thickness of marine deposits to repre- 

 sent a period of geologic time approximating in length that represented by 

 such other well-established systems as the Silurian and Devonian. They 

 were not founded primarily on fossil evidence, but on the physical criteria 

 of great series of marine deposits found wedging in between the under- 

 lying uneven top of older formations, which contain the now well-known 

 and altogether characteristic Upper Cambrian fauna, and the similarly 

 uneven base of another system that comprises the bulk and most char- 

 acteristic parts of the Ordovician system of the literature. The fossil 

 contents of the two new systems were, of course, immediately utilized in 

 recognizing the several formations from place to place. But the Ozarkian 

 and the Canadian faunas as such could be appreciated only after the 

 systems themselves had been discriminated by physical criteria. So far 

 as these faunas have been worked out they are clearly distinguishable and 

 as different from each other and from the preceding Cambrian and the 

 succeeding Ordovician faunas as are the organic remains in any succeed- 

 ing contiguous pair of. systems. In other words the Ozarkian fauna as 

 shown in Ulrich's collections in the U. S. National Museum is more 

 radically different from the life of the Upper Cambrian seas than is the 

 Silurian from the Ordovician, the Devonian from the Silurian, or the 1 

 Mississippian from the Devonian. The most striking feature of the 

 difference between the Ozarkian and the Cambrian is the strong develop- 

 ment of straight and curved cephalopods, and numerous coiled gastro- 

 3 



