1891.] 



NEW YORK ACADEMY OF SCIENCES. 



23 



entirely and affords a very beautiful slide. The olivine is seldom 

 fresh enough to be certainly identified, but as masses of a g-reen 

 alteration product are almost always pre.sent its occurrence is proba- 

 bly wide- spread. Professor Rosenbusch has, with characteristic 

 kindness, looked over some slides of certain of these dikes, and fully 

 indorses the determination of them as monchiquite, which had been 

 previously made by us. 



The following analyses illustrate the range in composition : — 



SiO., 



A 1,03 



Fe,03 



FeO 



CaO 



M-O 



K.p 



Na,,0 



Loss 



No. 2. 



40.37 



17.86 



14.45 



0.38 



17.61 



1.63 



0.83 



1.29 



4.47 



No. 14. 



4.5.13 



18.06 



11.88 



0.32 



10.17 



1.12 



6.06 



3.57 



3.04 



No. 21. 



44.30 



7.92 



25.38 



not (let. 



14.67 



1.98 



4.35 



99.39 



99.35 



98.60 



No. II also contains P^O^, 0.39. No. 2 and No. 14 were kindly 

 analyzed by Mr. W. H. Morrison, graduate student in chemistry 

 at Cornell University, and No. 21 by Mr. E. M. Chamot, assistant 

 in the same laboratory. The rocks are thus very basic and may, 

 as in No. 21, be very low in alkalies. 



The above-mentioned basic dikes and the bostonites are very 

 commonly associated with elaeolite-syenite, and we think they 

 furnish good reasons for anticipating the discovery of this rock in 

 the region of the Adirondacks. The dikes may, however, be an 

 extreme southern development of the great eruptive activity near 

 Montreal. We think their intrusion accompanied the upheaval of 

 the Green Mountains. 



During the field-work of the second summer Mr. A. S. Eakle, now 

 of the geological department of Cornell University, accompanied the 

 writers, and acknowledgments are due him for much valuable as- 

 sistance. 



Prof. Martin asked the lecturer if the smaller dikes might not 

 perhaps be regarded as originating from the larger ones. Prof. 

 Kemp replied that they could hardly be so regarded, and added 

 that the nearest large masses of eruptive rock were in the vicinity 

 of Montreal. 



Meeting adjourned. 



