232 New York State Museum 



The Ozarkian period is particularly marked by the 

 advent of cephalopods and a preponderance of mol- 

 luscan life. The Dicellocephalus fauna persisted, and 

 other derivations of Cambrian trilobites are no less 

 characteristic of the Ozarkian. Cephalopods (100 

 species), coiled and true patelloid gastropods and also 

 true cystids became prominent for the first time in the 

 Ozarkian. Gastropods have begun their ascendancy 

 and are represented by a fairly large number of genera. 

 It is the occurrence of a host of true gastropods and 

 cephalopods, of types entirely unknown in the true 

 Cambrian rocks, that stamps the Ozarkian as a new- 

 period in geologic history. The cephalopods became 

 abundant at some time in Missouri (Gulf fauna), but 

 somewhat later than the gastropods in Oklahoma 

 (Pacific). Pelecypods or bivalved mollusks and ostra- 

 cods among the crustaceans are wanting. Ozarkian 

 fossils are difficult to collect because most of the for- 

 mations are dolomitic. On silicification of the matrix, 

 however, good pseudomorphs are readily procurable. 

 One hundred and twenty-five species Tiave been listed, 

 and a great many more than this are known and in 

 course of description by Ulrich. The most prevalent 

 organisms of the Ozarkian were calcareous (lime-se- 

 creting) algae or seaweeds, known as Cryptozoon, oc- 

 curring as reef beds in the Hoyt limestone and Little 

 Falls dolomite, and strikingly exposed in Lester Park 

 and elsewhere in the Saratoga area in New York. 



Climate. The widespread occurrence of the reef- 

 making corallike animals of the Lower Cambrian, and 

 also the great numbers of individuals and variety of 

 species found among the trilobites and other classes 



