576 PROCEEDINGS OP THE PHILADELPHIA MEETING 



layers with the same minerals, all speak for this view of the case. New relays of 

 fluid masses would cause streams and vortices in the consolidating magma, and in 

 this way the " Schlieren," with their varying structure, would arise ; also the crush- 

 ing of feldspars and riebeckite cystals, which are cemented by the new substance. 

 The magma was extremely acid, fairly rich in aluminum, sodium, and potassium, 

 but the great quantities of titanium and fluorine have been brought by mineral- 

 izers, which were not rich in H 2 0, S, etcetera, but were characterized by abundance 

 of zirconium. As Lacroix remarks, zirconium has played a part in riebeckite 

 granites similar to that played by tin in cassiterite granites. 



To conclude, one may say that riebeckite rocks (and particularly those of the 

 granite-rhyolite series) have become solid under the following circumstances : A 

 very acid magma under high pressure and kept in motion by fresh arrivals of min- 

 eralizers, which are characterized by zirconium, fluorine, and titanium, and which 

 have been gradually absorbed and utilized for the formation of the constituents 

 of the rock, especially riebeckite and zircon. There was absence of past volcanic 

 activity, and the contact phenomena were reduced but characteristic. One could 

 suppose that this suggestion would come under the head of the phenomena con- 

 noted by piezocrystallization of Weinschenk. 



The paper of Doctor Murgoci was discussed by J. F. Kemp, H. S. 

 Washington, and the Chairman. 



Session of Saturday, December 31 



The Society met at 9.30 o'clock a m, President Branner in the chair, 

 The Secretary announced that the Council had decided to hold the 

 next annual meeting in Ottawa, Canada. 



The presentation of papers was declared in order, and the first paper 

 read was 



GEOLOG Y OF GREA T SLA VE LAKE 

 BY ROBERT BELL 



The second paper was 



NEW YORK DRUMLINS 

 BY H. L. FAIRCHILD 



[Abstract] 



A brief description of the drumlins of New York with reference to their distri- 

 bution ; altitudes or direction of major axes ; relation to the larger topography ; 

 relation to the underlying rocks ; composition; structure; form; size; origin. 



The paper was discussed by R. S. Tarr, A. C. Lane, and B. K. Emerson. 

 It will be published by the New York State Museum. 



