SIXTH REPORT OF THE DIRECTOR I909 1 37 



Relying on the fossil evidence just given it seems almost certain 

 that the Tribes Hill is at least as old and probably is older than 

 the dove limestone in division B of the Champlain " Calciferous." 

 This conclusion finds further good support in the fact that C r y p - 

 tozoon steeli, the principal fossil of division B, is found in 

 Pennsylvania above the Stonehenge limestone which there contains 

 the Tribes Hill fauna. 



Oscillations of level 



As detailed work has been carried forward in northern New 

 York during the past few years, the evidence has been steadily 

 accumulating to show that with a possible exception during 

 the late Ordovicic the Adirondack region remained steadily as 

 a land area, being sometimes an island, at other times part of a 

 much larger land. It appears further that frequent and often 

 very local oscillations of level effected modifications of its shore 

 line ; that the present erosion surface cuts the rocks in such w r ise 

 that the surface exposures are chiefly of the thinned, wear-shore 

 margins of many of the formations; that gaps in the succession 

 are frequent, and with much variation from place to place; and 

 that, because of these conditions, the New York section of these 

 rocks is very thin and very imperfect. From time to time Cush- 

 ing has summarized our knowledge of these oscillations. 1 With 

 each onward step in the detailed work, however, evidence of 

 further, and unexpected oscillations appears; and no doubt we 

 are, even now, acquainted with but a small proportion of them. 

 Nevertheless our present understanding of them should be sum- 

 marized. 



To begin with, no part of New York was submerged during 

 the Cambric. Lower Cambric deposits do occur locally within 

 the eastern edge of the State south of the Champlain valley but 

 it is highly probable that these are masses originally laid down 

 in a trough farther east and which were subsequently thrust 

 westward to their present position. The somewhat doubtful 

 Middle Cambric sediments found in Stissing mountain near 

 Poughkeepsie probably owe their present location to similar 

 thrusting. True Upper Cambric (St. Croixan) rocks are entirely 

 unknown within the State. Neither have such been found to the 



*N. Y. State Mus. Bui. 77, p. 51-65. 

 N. Y. State Mus. Bui. 95, p. 386-94. 

 Geol. Soc. Am. Bui. 19:175-76. 



