132 NEW YORK STATE MUSEUM 



togan of New York, particularly in the Hoyt limestone, is en- 

 tirely distinct from that found beneath the St Lawrence lime- 

 stone in the upper Mississippi valley, but some of the species 

 occur there in the overlying calcareous and arenaceous deposits 

 (St Lawrence limestone, Jordan sandstone and Oneota dolo- 

 mite), while all of them are included in the large molluscan and 

 trilobite faunas discovered by Ulrich in the middle divisions of 

 the Ozarkic in Missouri. Most of them occur there in the Gas- 

 conade chert, which is the third from the top of the seven 

 formations into which the Ozarkic in Missouri is divisible. All 

 of these formations succeed the Bonneterre limestone and Davis 

 shale, which carry the St Croix and Reagan fauna that is so widely 

 distributed -in the Mississippi valley, in the Rocky mountains 

 and in Texas, and which Ulrich, chiefly on diastrophic grounds, 

 regards as marking the closing stage of the Cambric in Amer- 

 ica. If this is not conceded then there is no sufficient reason 

 for drawing the upper boundary of the Cambric system beneath 

 the top of the Ordovicic — which would go back to Sedgwicks's 

 original conception of his Cambric — nor for recognizing more 

 than a single system in the Neopaleozoic, another in the Meso- 

 zoic and a third in the Neozoic. If the Devonic is recognized 

 as a system distinct from the Siluric on the one side and the 

 Waverlyan on the other then the Ozarkic is no less distinct 

 from the preceding " Cambrian " and the succeeding Canadian 

 system ; and the Canadian is equally distinct from the Ordovicic. 

 If the criteria relied on are deemed sufficient in any of these 

 instances then they are equally sound and worthy of considera- 

 tion in all the others. 



The boundary between the Cambric and the Ozarkic as here 

 drawn is everywhere recognizable and the contacts between the 

 Ozarkic and the Canadian, and between the Canadian and the 

 Ordovicic are likewise definite. This is because they are de- 

 termined by diastrophism. But no one has yet succeeded in 

 drawing a satisfactory boundary between the upper limit of the 

 range of " Cambrian " trilobites and the lower limit of the 

 " Ordovician " gastropods and cephalopods. In fact there is 

 no such boundary, since the latter were well established before 

 the middle of the Ozarkic, and Cambric types of trilobites sur- 

 vived through the Ozarkic into the Canadian and a few even 

 into the Ordovicic. Of course, neither the beginning nor the 

 closing deposits of these Eopaleozoic systems are even approxi- 



