32 NEW YORK STATE MUSEUM 



miles long and not over one-half of a mile wide and must be sill-like 

 in nature. The northwestern mass of fine-grained granite is now 

 being exposed by erosion of a domed series of overlying beds of 

 Grenville gneiss, while the strikes of the beds around a similar 

 mass of fine-grained granite south of Lake Bonaparte are parallel 

 to its border. 



The syenite bears intrusive relations to the gabbro, while the 

 syenite itself is intruded by granite dikes offshooting, presumably 

 from the porphyritic granite, from the fine-grained granite, and 

 from its own granitic differentiate as the case may be. 



Four small patches of Potsdam sandstone remain as outlying 

 remnants within the central belt of the Grenville series, resting 

 unconformably on the lower eroded levels of the marble beds. 



Thoroughgoing cataclastic metamorphism of a portion of the 

 syenite mass, as well as of dikes of hyperite and granite cutting 

 this mass whose cleavage is parallel to that of the inclosing rock, 

 together with the regional trend of the formations, shows unmis- 

 takably the evidence of intense, long-continued orogenic forces pre- 

 viously acting in this region. The minor evidence of cataclastic 

 structures in the Grenville gneisses may be partially explained by 

 subsequent igneous metamorphism. A possible variation in the 

 effect of these forces distributed according to the geographical 

 location and character and age of the rock is being investigated. 

 Other important data with respect to the gneissic structures will 

 be given later. 



SURFICIAL GEOLOGY 



The glacial phenomena of the Catskill mountains. The 



investigation of the glacial geology of the Catskills was begun 

 during the past summer by Dr John L. Rich, and included a 

 reconnaissance of the region as a whole and a semidetailed map- 

 ping of its glacial features directed toward the outlining of the 

 major events of its glacial history and a determination of the 

 problems for whose solution more detailed examinations might be 

 required. 



All the higher mountain region, except a small section south 

 and southwest of Arkville, was studied, and, in addition, reconnais- 

 sance surveys were carried down the west branch of the Dela- 

 ware river to Delhi, thence up the little Delaware to Lake Dela- 

 ware, and also south of the mountains into the upper branches of 

 Neversink and Rondout creeks. The area examined included the 

 whole of ■ the Phoenician and the mountainous parts of the 



