STRATIGRAPHIC TAXONOMY 591 



as in the late Niagaran-Onondaga contact at Louisville, Kentucky, and 

 at Newsom, Tennessee, and in the similar contacts of Silurian and De- 

 vonian beds at Buffalo and elsewhere in 'New York — illustrations cited 

 b}^ Schuchert and generally accepted by geologists as satisfactorily estab- 

 lished cases of long but inconspicuously marked time breaks. Under the 

 circumstances, especially since stratigraphers are now practically a unit 

 in placing the Helderbergian at the base of the Devonian, it seems to me 

 w^e should insist on consistent treatment of all such cases. In other 

 words, if the Helderbergian is Devonian and the Lowville is the lower 

 part of the Black Eiver group, then the Eichmondian is Silurian, the 

 Keyser is Helderbergian, the Warsaw is Tennessean, and the Sainte Gene- 

 vieve is early Chesterian. 



In applying the principle of introductory deposits to parts of forma- 

 tions, particularly wlien the underlying formation is of clastic matter and 

 the overlying of limestone, general practice has been far from consistent. 

 As a rule, however, these inconsistencies have resulted through lack of 

 data and information. With plenty of determinative fossils, a mistake 

 of this kind is unlikely. Without good fossil evidence, positive deter- 

 minations are often difficult, but it is seldom indeed that close study 

 of the structural relations of the ^^passage" beds fails to solve the taxo- 

 nomic problem. 



It may be set down as a general proposition that when a break in sedi- 

 mentation is indicated at the base of a clastic bed whose top grades, with- 

 out evidence of interrupted submergence, slowly or rapidly into less clastic 

 deposits, then the new formation or group should include the former as 

 an initial deposit, even though it is lithically much more like the under- 

 lying formation than it is like the overlying sediments. The Kiefer 

 sandstone in Maryland affords an excellent illustration. This sandstone 

 has hitherto been referred to as the top member of the Clinton. On 

 investigation it was established that the Kiefer is a locally developed 

 deposit, that it passes without break into the overlying sandy shales of 

 the McKenzie formation, and that it is bounded below by an unconform- 

 ity which in places cuts out the Rochester member or formation of the 

 Clinton group. The intervening hiatus is regarded as representing the 

 upper or Chicago group of the Niagaran series. On these grounds, which 

 are supplemented by good faunal evidence, the Kiefer sandstone is now 

 classified as a local basal member or facies of the McKenzie formation. 



The Hardin sandstone in west central Tennessee and the Sylamore 

 sandstone in north Arkansas are similarly referred to the Chattanooga 

 shale. These, however, are true basal deposits of a widely overlapping 



