1 128 PRINCIPLES OF STRATIGRAPHY 



provinces of Canada. In the latter region is likewise found a more 

 complete representation of the Upper Cambric formations than 

 has yet been ascertained to exist in the State of New York. 

 It is on this account that the East Canadian names Bretonian, 

 Acadian and Etcheminian {cf. Georgian) iiave been used for the 

 Upper, Middle and Lower Cambric, respectively. (Grabau-17.) 



Again, a hiatus exists in Nevv' York between the Ordovicic and 

 Siluric, the upper part of the Ordovicic not being represented, at 

 least not by fossiliferous formations. The lower Siluric, too, is 

 less satisfactorily represented in New York than elsewhere, for, 

 as currently understood, it begins with a sandstone formation, the 

 Medina, which is a shore formation, where not of non-marine origin. 

 For the Upper Ordovicic and Lower Siluric, then, the New York 

 column has to be pieced out by formations developed elsewhere, 

 the standard selected being the Cincinnati group of the south-cen- 

 tral states for the one, and the lower Mississippi region for the 

 other.* Even within the lower Ordovicic there is an incomplete 

 representation of the top of the Beekmantown and of the Chazy for- 

 mation, this incompleteness being measurable by thousands of feet of 

 limestone in the Mohawk A'alley, but by very much less in the Lake 

 Champlain region. The Salina of New York, of Mid-Siluric age, 

 also forms an unsatisfactory member of the standard series, as al- 

 ready pointed out, since it represents abnormal conditions of sedi- 

 mentation. Aside from these, however, the New York column 

 represents an eminently satisfactory standard of the Palaeozoic 

 formation below the Mississippic. 



The standard American series for the Mississippic is that of the 

 Mississippi \'alley, though that is not itself a complete section. 

 The standard marine sections for the Carbonic and Permic have not 

 yet been fully worked out for this country. The former is found 

 in Kansas, Missouri and Arkansas ; the latter in Texas. No Ameri- 

 can Triassic or Jurassic standards are recognized, the fragmentary 

 development of these formations being referred to foreign stand- 

 ards. The Comanchic and Cretacic, on the other hand, are well 

 represented by formations in Mexico, Texas and the Great Plains 

 region, which localities have furnished the standard sections. The 

 Comanchic is well represented in the southern areas, but the sections 

 of the typical Cretacic in the standard region (Colorado and Mon- 

 tana) are incomplete at the bottom and at the top, where they 

 include non-marine formations, i. e., the Dakota sandstone, and the 



* The Anticosti section promises to be one of the most perfect North American 

 Lower Siluric (Niagaran) sections, but it is not as yet certain in how far this 

 section belonged to a distinct geographic province. (See Schuchert-39 :5J2.) 



