REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r65 



As a result of reconnaissance work in 1890, Van Hise came to 

 the conclusion that the Adirondack pre-Cambrian comiprises '' a 

 core of eruptive basic rock, which has upthrust and intruded 

 itself within the gneissic fiieries. Because of the character of the 

 gneissic eeries, containing quartz schist, graphite schist, and 

 crystalline limestone, including graphite, it is regarded as having 

 been originally clastic. Its present crystalline character and 

 quaquaversal arrangement is doubtless due to the intrusion of 

 the gabbro. . . The lowest coarse grained gneies, inferior to 

 the limestone, perhaps belongs to a still earlier series, but thie 

 is a point upon which closer studies are needed."^ 



During the progress of the later Adirondack work we have 

 been finding considerable fault with this nummary of Van Hise's. 

 Most certainly, if the eruptive core be limited to the gabbro rocks, 

 the statement is wide of the mark, nor is the assertion of a 

 quaquaversal arrangement of the gneisses found to accord with 

 our observations on dip and strike. But, if the syenite and 

 granite be included in the eruptive series in addition to the 

 gabbro rocks, then the sitatement in respect to the eruptive 

 core comes much nearer to representing the real state of things; 

 though, since the eruptives are themselves heavily metamor- 

 phoeed, their invasion can not be regarded as the sole, or perhaps 

 not even as the main cause of the crystalline character of the 

 gneisses. If they be included, then the great central mass of 

 the Adirondack^ does consist of an eruptive complex, anoirtho- 

 fiite on the east and north, syenite and granite on the south, west 

 and north, eruptives which have invaded the gneisses from 

 beneath. Kemp, in a recent valuable paper on pre-Cambrian 

 sediments in the Adirondacks,^ has emphasized the massing of 

 the limestones and clastic gneisses on the southeast and north- 

 west. While in a general way this is true, small outcrops of these 

 rocks are more numerous in the heart of the region than the 

 published data at Kemp's disposal when has paper was written 

 led him to believe. These patches are of small extent and occur 



^ Van Hise, O. R. U. S. geol. sur. Bui. 86: 398-99. 

 ^ Science. New ser. 12: 81-98. 



