Boston 3teeting of the Geological Society. ^15 
talline limestones, and ophicalcites. Next in age, penetrating both 
these, is found the great series of igneous rocks of the gabbro family, 
which chiefly make up the Adirondacks. Still later are the Paleozoic 
sediments, of which the Potsdam is the oldest. 
The gabbros were shown to include nearly pure aggregates of labra- 
dorite at one extreme, which were called anorthosites in accordance 
with Prof. F. D. Adams' precedent, and quite basic olivine-gabbros at 
the other extreme. Between these two almost every gradation is met, 
but the anorthosites favor the main mountain masses, while the basic 
gabbros occur more as outliers. All exhibit most remarkable effects of 
dynamic metamorphism, such as crushing and brecciation," develop- 
ment of gneissoid structure, change of pyroxene to hornblende, etc. 
Remarkable reaction-rims that surround olivine, pyroxene and titanif- 
erous magnetite, where coming next to feldspar, were especially dwelt 
on, and the parallels occurring elsewhere were cited. Quite extended 
mention was also made of the contact phenomena where the gabbros 
penetrate the limestones. The paper concluded with a brief review of 
the other known gabbro areas in North America, and especially of the 
Canadian exposures described by Prof. Adams, with whose Morin dis- 
trict the Adirondacks stand in very close relations. Acknowledgments 
were made to Prof. James Hall, state geologist, and Dr. P. J. H. Merrill, 
director of the N. Y. State Museum, for permission to use the materials 
which were chiefly gathered under their direction. 
42. Notes on the occurrence of mica in the Laurentian of the Ottawa 
district. Robert W. Ells, Ottawa, Canada. (Read by title.) A brief 
discussion of the geological relations of the Laurentian rocks, with de- 
scription of certain peculiarities as to their occurrence, observed in the 
townships of Hull, Wakefield and Templeton, and at points along the 
Gatineau and Du Lievre rivers. 
43. Intrusive sandstone dikes in granite. Whitman Cross, Wash- 
ington, D. C. (Read by title.) In the area of the Pike's Peak granite 
■mass, in Colorado, there occur sandstone bodies whose formal relations 
to the granite are perfectly analogous to those of dikes of igneous rock, 
while the substance of the masses in question is purely a clastic mix- 
ture, almost wholly of quartz, of fine and even grain, very smiliar to 
sandstones of sedimentary origin. These rocks and their occurrence 
were described and illustrated by hand specimens. 
44. Age of the Auriferous slates of the Sierra Nevada. James P. 
; Smith, Palo Alto, Cal. The Auriferous slates have been assigned to 
various ages, ranging from Paleozoic to Cretaceous. The various 
known localities for fossils in these slates are discussed, their horizons 
are determined, and new information is added about certain Carbonif- 
erous, Triassic. and Jurassic localities. The Mariposa slates are ascer- 
tained by paleontologic evidence to be of upper Jurassic age, probably 
lower Kimmeridge. The Aucel la -bearing beds of California are dis- 
cussed, and found, after the analogy of the An eel la bearing beds of 
Russia, to range from the topof the Oxford, upper Jura, to the Neocom- 
ian, lower Cretaceous. Neumayr's theory of climatic zones is shown 
not to apply with exactness to the Jura of California. The uplift and 
metamorphism of the Sierras and Coast range are thought to have 
taken place in late Jurassic time. 
15. Origin of the coarsely Crystalline vein granites <n- pegmatites. 
William O. Crosby, Boston, Mass. The leading idea of this paper is 
that the pegmatites or giant granites are the product of neither solu- 
tion (veins) nor fusion (dikes), but of the more perfect co-operation of 
heat and water in what may be called aqueo-igrneous fusion and igneo- 
aqueous solution. We may assume that, whatever may be true of other 
igneous rocks, water has contributed to the liquefaction of the micace- 
ous granites, with which the pegmatites are so generally associated. 
During the extremely slow, centripetal cooling ami solidification of a 
