224 J. F. KEMP — GABBROS OF LAKE CHAMPLAIN. 



ous intrusions are found * Scapolite is especially characteristic of -nch, 

 and invariably with it are hornblende, pyroxene and titanite. 



Conclusions. 



The exposures treated in the above pages illustrate again the varia- 

 bility of great masses of gabbroitic rocks and the rapid changes from 

 place to place which they so frequently show, both in mineralogy and 

 structure. This has been already noted by G. H. Williams, F. D. Adams 

 and others. We need not be surprised to find examples extending from 

 quite pure feldspathic aggregates to basic gabbros, and even, as in the 

 Baltimore and Peekskill exposures, to peridotites and pyroxenites, but 

 at the same time the close genetic relations of such rocks cannot be too 

 strongly emphasized by petrologists. The wide distribution of the reac- 

 tion rims, corrosion zones, crowns, aureoles, et cetera, call them as we 

 may, is also worthy of remark, as so many gabbros show them in vari- 

 ous parts of the world. The same is true of the bodies of iron ore which 

 mark the extreme phase of basic development, although in relatively 

 limited amount and of very local character. In many places the contact 

 effects of these intrusions on limestones are so similar that one is inclined 

 to suspect the near presence of igneous rocks wherever these contact 

 minerals, and especially scapolite, are reported in limestone. 



♦Compare J. F. Kemp : On Van Artsdalen's Quarry, Bucks County, Pennsylvania. Trans. N. Y. 

 Acad. Sci., vol. xii, 1892, p. 19. Kemp and Holliek : On the Granite of Mount Adam and Mount Eve, 

 Orange County, New York, and its Contact Phenomena. Annals of the N. Y. Acad. Sci., vol. viii, 

 January, 1894. 



Not a few similar cases are cited by Lacroix in the paper on " Gneiss a pj'rox^ne et des roches a 

 wernerite,'" to which frequent reference has been made above. 



