TITLES AND ABSTRACTS OF PAPERS 45 



tion of the original material by the magmatic solution rather than those of a 

 violent intrusion. The observed relations are very similar to those which 

 foreign geologists have described as due to lit-par-lit injection, and the mode 

 of operation is believed to have been essentially the same. 



Certain features observed in the gneisses imply characteristics of the magma 

 which at first sight do not appear mutually concordant. Thus the degree of 

 viscosity implied by the presence of thinly tabular sheets of inclusions within 

 the granite, standing nearly upright and unsupported except by the magma 

 on either side, does not harmonize with the facility with which magmatic 

 material has been transfused into the adjacent rock. In trying to reconcile 

 these apparently antagonistic features inquiry has been directed toward a con- 

 sideration of certain of the properties of magmatic solutions. The question 

 of the critical temperatures of volatile substances is discussed in its bearing 

 on their condition within the magma. Further, the problem of a possible 

 differentiation of a magma when injected into a wall rock in a multitude of 

 adjacent streams is taken up, as related to the views expressed by the foreign 

 advocates of lit-par-lit injection. On this matter our knowledge of the physical 

 and chemical properties of magmas is deficient in so many respects that very 

 positive statements can not be made, but it appears that under the conditions 

 of injection such a differentiation as has been assumed would probably take 

 place. By this means the advance of the main body of magma would be 

 preceded by that of a more dilute portion, which would be able to impregnate 

 the wall rock with facility and initiate processes of transformation and solu- 

 tion which the more concentrated body following would carry farther toward 

 completion. 



Eead in full from manuscript. 



Discussion 



Dr. J. V. Lewis : In my experience in the New Jersey Highlands it has 

 seemed that two distinct types of parallel structure exist there — this lit-par-lit 

 injection which Doctor Fenner has brought out so interestingly and an indis- 

 tinct gneissic appearance which some of us have thought of as perhaps a sort 

 of internal flow-structure. I should like to ask Doctor Fenner whether it is 

 possible to make this distinction in the region of his studies. 



Further remarks were made by Messrs. J. P. Iddings and James F. 

 Kemp. 



MAGMATIC DIFFERENTIATION AND ASSIMILATION IN THE ADIRONDACK 



REGION 



BY WILLIAM J. MILLEB 



(Al>stract) 



The deep-seated condition to which the present surface rocks of the pre- 

 Cambrian area in northern New York were subjected when the tremendous 

 molten masses were intruded into the thick Grenville sediments were decidedly 

 favorable for both magmatic differentiation and assimilation. Probably few 

 regions present any better opportunities for the study of such phenomena. It 



