140 NEW YORK STATE MUSEUM 



posit, which nearly everywhere in the Mohawk valley rests on the 

 Little Falls. In the Black river valley, where the Little Falls is 

 absent, it rests on the Theresa formation. It is absent at Middle- 

 ville and Newport, in the West Canada creek valley, showing that 

 there, at least, it did not extend as far northward on the Adiron- 

 dack oldland, as the Little Falls did. It is absent also at Saratoga, 

 indicating that there also we are beyond its shore line. The exact 

 equivalent of the Tribes Hill seems not to occur in the Champlain 

 valley. At any rate its peculiar fauna has not been observed there. 

 Apparently it is older than the fine grained limestone of division B 

 with which the revised Beekmantown begins in the Champlain val- 

 ley. Judging from the evidence now available the Tribes Hill 

 submergence formed a geographic pattern quite different from that 

 of the preceding Little Falls sea. The latter covered the southern 

 and eastern flanks, the Tribes Hill occupied more limited embay- 

 ments on the southern and western sides of the Adirondack area. 

 The depression at the west was short-lived, uplift following with in- 

 creasing eastward tilting, giving rise to long continued submergence 

 of the Champlain valley. By the close of Tribes Hill time the up- 

 lift involved all the Mohawk region proper, the remaining divi- 

 sions of the Beekmantown limestone being confined to the Cham- 

 plain valley trough and its northern and southern prolongations. 

 The upper Beekmantown is found to the north in the Ottawa valley. 

 To the south Beekmantown deposits are recognized at intervals 

 through southeastern New York, New Jersey and Pennsylvania. 

 Although the Beekmantown is of extraordinary thickness in the 

 last state (2000 to 4200 feet) even the thickest sections still indi- 

 cate occasional interruptions in sedimentation and probably with- 

 drawal of seas. 



At the close of the Beekmantown uplift again occurred, producing 

 the unconformity between it and the Chazy, in the Champlain valley. 



We have evidence also of a number of hitherto unsuspected os- 

 cillations of the general region during the succeeding Black River 

 and Trenton times. Since, however, we are here concerned chiefly 

 with the lower formations, those are left for discussion elsewhere. 



