Ravmoxu : The Chazy Formation axi> ris Fauna. 571 



north and south line as a check. It is known, however, that the thick- 

 ness of Division i at Valcour Island is 300 feet, and of the same divi- 

 sion at Crown Point is o, a thinning of 7.3 feet per mile. If this 

 factor is not correct, it is too small. Taking this as a basis, the base 

 of the Crown Point section is at least 300 feet above the base of the 

 Valcour Island section, and the base of the Orwell section at least 424 

 feet above the base of the Valcour Island section. (See Fig. 3. ) 



If this minimum estimate of the height of the base of the Crown 

 Point section above the base of the Valcour Island section be used, it 

 will be seen that the Crown Point section lacks the upper 285 feet of 

 the formation. This is a gradient, to the top of the beds at Valcour 

 Island, of 6.95 feet per mile. Taking the base of the Orwell section 

 at 424 feet, the upper 407 feet are lacking. The thinning in the 17 

 miles from Crown Point to Orwell is 122 feet, or 7.1 feet per mile, 

 while the gradient to the top of the Chazy at Valcour Island is 7.01 

 feet per mile. The close correspondence of these gradients and the 

 small gradient, 7 feet per mile for a distance of 58 miles, are signifi- 

 cant and seemingly indicate a base leveled land during the Chazy- 

 Lowville interval. 



Representation of Chazy Time in Other Regions. 



The Chazy was formerly identified by various geologists as covering 

 a large area, extending south along the Appalachian Mountains as far 

 as Georgia, and occurring in Kentucky, Wisconsin, Michigan, Min- 

 nesota, and in the southern part of the Rocky Mountains. More 

 recently it has been held that while certain formations may have been 

 laid down during Chazy time, the typical Chazy rocks and fauna are 

 restricted to the region of the Champlain and Ottawa Valleys and the 

 Mingan Islands. Among the formations correlated in time with the 

 Chazy are the St. Peter sandstone, the lower part of the Stones River 

 group, and the Blue I-imestone of Lenoirs, Tennessee. 



The St. Peter Sandstone. — This formation has long been corre- 

 lated with the Chazy. It is best developed in Minnesota, Wisconsin, 

 Iowa and Illinois, where it underlies the lowest member of the Mo- 

 hawkian series. The fauna of this formation, described by Sardeson 

 (Bulletin of the Minnesota Academy of Sciences, volume V\ , number 

 I, part I, page 64, 1894), consists principally of mollusca, which 

 have a decided affinity with Mohawkian forms. None of the species 

 are found in the typical Chazy. This fauna, in the neighborhood of 



