REPORT OP THE DIRECTOR AND STATE GEOLOGIST 1901 r27 



esting from another standpoint, that of its probable age and 

 associations. Its surroundings permit no more definite asser- 

 tion concerning its age than that it must be younger than the 

 Hudson slates which it cuts. This renders a reference to the 

 pre-Cambrian diabase of the region impossible, though there is 

 a strong resemblance in the rocks. There remain the basic 

 eruptives of the Champlain and Mohawk valleys and the traps 

 of the Trias, as representatives of the only known periods of 

 vulcanism of post-Ordovician date in the region. The rock must 

 either be referred to one or the other of these, or else must stand 

 by itself as the single representative of a heretofore unknown 

 time of igneous activity, a most unlikely though not impossible 

 contingency. 



The eruptives of the Champlain valley are younger than the 

 Utica shale of the Ordovician, though their precise age is un- 

 known. They comprise both acid (bostonites) and basic (camp- 

 tonites, monchiquites and fourchites), basaltlike rocks, of the 

 sort usually found in association with nephelin syenite eruptives, 

 such rocks occurring in Canada directly to the northward. With 

 the exception of one single dike noted by Kemp, none of these 

 rocks are diabases, though the known number of basic dikes is 

 large, and it would therefore seem to be at least an open ques- 

 tion as to whether this dike should be properly classed with the 

 remainder. 1 Its nearly north-south trend is certainly excep- 

 tional for the region, and it may be a stray dike of Triassic age. 



The eruptives of central New York are all exceedingly basic 

 rocks, alnoites and peridotites. Smyth's recent discovery of 

 melilite in the Syracuse rock would seem to indicate the proba- 

 bility that all of these rocks may prove to be alnoites. 2 The 

 dikes about Manheim cut Ordovician rocks, those at Syracuse 

 cut the Silurian, and, if the dikes at Ithaca belong to the same 

 group, a late Paleozoic age is indicated for all, since these cut 

 the Upper Devonian. 3 They are so utterly different in character 



X U. S. Geol. Sur. Bui. 107, p. 48. 



2 Am. Jour. Sci. ser. 4. 14:26-30. 



^Kemp, J. F. Am. Jour. Sci. ser. 3. 42-410. 



