Synopsis of Author’s previous Investigations.

At the Boston meeting of the Geological Society a year ago the writer presented a sketch of the gabbros which are so plentifully developed in the eastern portion of the Adirondacks. In the introductory part of the paper it was stated that the general geology of this region consisted of (A) a series of quartz-orthoclase (mostly microperthitic) gneisses, which may contain also hornblende or biotite or augite and at times much plagioclase; (B) a series of crystalline limestones often shading into ophicalcites on the east and closely involved with black hornblendic and pyroxenic schists and gneiss, and (C) a great series of intruded plutonic rocks of the gabbro family (anorthosites, gabbro proper, olivine gabbro and norites) which penetrate both the others and are doubtless of later date. The variability of the augitic gneisses in series A was further commented on and the difficulties they present . . .

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