242 J. F. KEMP — ROCKS OF THE EASTERN ADIRONDACKS. 



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 plu- 

 tonic 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 in the way of 

 correlation were emphasized. While likely to be more or less modified 

 in a minor way, the above grouping will probably stand in its essentials. 



Scope of the Paper. 



It is the purpose of this paper to outline the characters of the crystal- 

 line limestones, ophicalcites and associated schists and to set forth briefly 

 the evidences for believing them to be intermediate in age between the 

 gneisses and the gabbroic rocks. The difficulty of drawing a sharp line 

 between the gneiss and the limestone series arises from the fact that the 

 latter may be a phase of the upper portion of the former, although their 

 petrographic characters are in marked contrast. 



Geographic Distribution of the Rocks. 



In general it may be said that the increasing record of observations in 

 the region seems to corroborate that conception of the mountains as a 

 whole which was briefly sketched by Van Hise in the bulletin on the 

 correlation of the Archean and Algonkian, and which was formed during 

 his reconnoissance with Walcott and Pumpelly. This conception in- 

 volves a central intrusion of igneous rocks with a fringing rim of older 

 gneisses, schists, limestones, etcetera. 



It would be nearer the exact truth to regard the intrusions as being 

 in several more or less parallel ranges, with remnants of the others in the 

 valleys between and on the flanks. The anorthosites, for instance, are 

 now known to occur over a northeast-and-southwest distance of about 

 120 miles (that is, from Keeseville to Little Fails), and over a distance 

 at right angles to this varying from 80 miles as a maximum. In addition 

 to this, H. P. Gushing has discovered north of Keeseville at least one 

 outHer, a description of which he has in course of preparation. 



Near mount Marcy the central nucleus is best developed. It consists ^ 

 of a great group of peaks, the highest in the state, which are composed 



