STRATTGRAriTIC TAXONOMY C)?)l 



and at Beauharnois, near Montreal, Canada. Judging from these occur- 

 rences, the Ozarkian continental seas attained their maximum distribu- 

 tion at this time. 



Proctor dolomite. — This is the third formation of the system as devel- 

 oped in Missouri. The formation is easily recognized by its non-siliceous, 

 massive beds, the absence of chert at this horizon causing it to stand out 

 conspicuously between the two profusely cherty formations which sharph 

 define it above and beneath. The formation is best developed in Morgan 

 and Miller counties, where it attains a thickness of about 60 feet. In 

 Shannon and Carter counties it is much thinner and seems to be absent 

 locally altogether. As usual with non-cherty dolomites, fossils, if not 

 wholly absent, are at least very scarce in the Proctor. 



Gasconade formation. — This formation (Buckley; middle part only of 

 Gasconade of Bain and Ulrich) is the next above the Proctor. Like the 

 Gasconade, it is easily distinguished in Miller and adjoining counties, 

 where it attains a thickness of approximately 265 feet, and consists 

 almost entirely of profusely cherty dolomite. -In these counties the 

 base of the formation is formed by a sandstone — the "Third sandstone" 

 of Swallow, the Gunther of Buckley — which rests unconformably on 

 the otherwise very different Proctor. The top also is not difficult to 

 find here, being overlain by the sandstones and conglomerates of the 

 Koubidoux. However, on the eastern and southern sides of the Ozarkian 

 area, neither the Gasconade nor the Proctor is conspicuously developed, 

 so that, in the absence of fossils, it is sometimes difficult to distinguish 

 this formation from the Eminence, or even to decide whether it is present 

 at all. In the latter regions again the Eoubidoux is not typically de- 

 veloped. Possibly it is absent; or, if present, it grades upward into the 

 Jefferson City. The upper boundary of the Gasconade also may there- 

 fore be obscure locally. Still, to any one knowing the fossils and able to 

 find them, satisfactory separations are readily possible, for the three 

 faunas (Eminence, Gasconade, and Roubidoux-Jefferson City) are very 

 different. 



The Gasconade fauna is a large one, but not altogether new. Indeed, 

 it is a few species of this fauna that Hall in 1847 and Cleland in 1903 

 described from the chert beds at the top of the Little Falls dolomite at 

 Little Falls, New York. Among these New York fossils is Helicotoma 

 (EuomplialiLs) uniangulata, the most distinctive and best of the Gas- 

 conade guide fossils. So far as I can make them out, all the other species 

 described by Hall and Cleland from the chert at Little Falls occur 

 also in Missouri. Several species of this fauna have been found near 

 Whitehall, New York, and four, in part the same species, a few miles 



