SIXTH REPORT OF THE DIRECTOR I9O9 l^l 



inland troughs and basins to Canada. In the Mississippi valley 

 and in central Texas its deposits covered about the same areas 

 previously held by the late Cambric sea. It is this Ozarkic sea 

 that rather early in its history surrounded the Adirondack 

 uplift, laying- down first the Potsdam, then the Theresa and 

 finally, when conditions had become fairly quiescent and estab- 

 lished, the Little Falls dolomite. However, long before the 

 close of the Ozarkic the waters were again withdrawn from 

 New York into reconstructed Appalachian troughs, remaining 

 also in the but slightly modified basins of the Mississippi valley. 



The more essential features of the evidence on which this 

 interpretation is based may be briefly stated as follows: (i) The 

 stratigraphic relations of the Potsdam to the Theresa and of 

 this to the Little Falls indicate a practically uninterrupted 

 sequence of sedimentation. There was gradual reduction of 

 adjacent land areas, and there may have been slight oscillations, 

 but there is no evidence of a break in deposition nor of change 

 in its character that may not be explained as of purely local 

 significance. (2) So far as known there are no deposits cor- 

 responding in age to the Upper Cambric in the Mississippi 

 valley in areas intervening between this valley and the Adiron- 

 dack region ; neither have any been discovered in the middle 

 part of the Appalachian valley nor in the Atlantic province ; 

 hence there is no means of directly connecting the Potsdam- 

 Little Falls deposits and faunas with true Upper Cambric life 

 and sediments elsewhere. (3) The Potsdam and Little Falls 

 are clearly recognizable in the Allentown formation (Ulrich) in 

 central and northeastern Pennsylvania and in the lower and 

 middle divisions of the Knox farther south in the Appalachian 

 valley. The Allentown rests on Lower Cambric, both Middle 

 and Upper Cambric being absent in its area. The probably 

 equivalent Conococheague formation of the Cumberland valley 

 in southern Pennsylvania, contains a Saratogan fauna but differs 

 lithologically and is underlain by two Middle Cambric forma- 

 tions. The lower Knox is underlain by a thin Upper Cambric, 

 considerable Middle Cambric and some Lower Cambric, the 

 southern Appalachian Cambric section being relatively com- 

 plete. Each of these Appalachian Ozarkic formations is over- 

 lain by from 1000 feet to 4200 feet of Canadian (emend. Ulrich) 

 limestone and dolomite, represented in eastern New York by 

 the Beekmantown. (4) The fauna so far discovered in the Sara- 



