REPORT OF THE DIRECTOR IQII 2^ 



A part of the field season was devoted to a detailed survey of 

 the northwestern portion of the Lake Pleasant quadrangle. Not 

 enough work has been done to justify any general conclusions for 

 the quadrangle but, in the region so far examined, the Grenville 

 series is only scantily represented, the few small areas noted being 

 not much more than inclusions in the igneous rocks. Only one 

 outcrop of crystalline limestone has been observed. 



The great rock masses are syenite (augitic to hornblendic), gran- 

 itic syenite, granite (pink to gray), and granite porphyry. These 

 rocks all appear to be differentiation products of the same cooling 

 magma. They grade from one type to another so frequently that 

 drawing the boundary lines in such a rough, wooded country is 

 difficult work. 



Another rock encountered in fairly large masses is a fine-grained, 

 gray to pinkish gneiss which, at times, shows suggestions of a banded 

 structure. The relation of this rock to the others has not yet been 

 satisfactorily determined. 



No gabbro or diabase dikes have been noted, but the occasional 

 gabbro boulders in the vicinity of Lake Pleasant indicate that this 

 rock Occurs not far northw^ard. 



Valcour Island. The detailed study and survey of this island in 

 Lake Champlain, its rocks and their contents, its origin and bearing 

 on the general history of the lake basin, have been carried forward 

 by Prof. George H. Hudson. 



Southeastern New York. During the past year there has been 

 issued Doctor Berkey's important bulletin on the Geology of the 

 New York (Catskill) Aqueduct wdiich has been in large demand 

 from engineers and other students of practical geological problems. 

 The continuation of the aqueduct operations has afforded oppor- 

 tunity to examine the many tunnels and open cuts now nearly at 

 maximum development and to make comparison with the conclusions 

 of earlier explorations. This has been done with considerable care, 

 with particular attention to sections where detail of structure could 

 be worked out. It is only fair to say that there have been no wholly 

 unlooked for conditions yet discovered. The geological formations 

 and structures and conditions already described and based upon pre- 

 liminary explorations, need little modification from the completed 

 work. It is possible, however, now to class a great many items as 

 facts that have heretofore been given as interpretations, and many 

 details can now be added. The existence of several mud-filled caves 

 in the limestones of the Rondout valley to greater depth than one 



