214 J. F. KEMP — GABBROS OP LAKE CHAMPLAIN. 



field of observation than the immediate text would indicate. The work 

 will be continued with annual increments of mapped territory. For 

 clearness a brief preliminary sketch of the geology of the Adirondacks 

 is given. 



Review of the Geology of the x\dirondacks. 



The best known part of this region lies in Clinton, Essex and Warren 

 counties on the east, although even this has been but little explored since 

 the time of Ebenezer Emmons. Of the great stretches of the " North 

 Woods," in Hamilton, Herkimer, Lewis, Saint Lawrence and Franklin 

 counties, much less has been recorded. In the west Professor C. H. Smyth, 

 Jr., of Hamilton College! is working under Professor Hall, and in Clinton 

 and Franklin counties Professor H. P. Cushing, of Adelbert College, 

 as assistant to the writer — likewise under Professor Hall. There is 

 evidence going to show that we have (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 crys- 

 talline limestones, often shading into ophicalcites on the east and closely 

 involved with black, hornblendic and pyroxenic schists and gneisses ; 

 and (C) a great series of intruded, plutonic rocks of the gabbro family 

 (anorthosites, gabbro proper, olivine gabbros, and norites) which pene- 

 trate both the others and are doubtless of later date. The last named 

 series has suffered (as beyond question the others have also) such ex- 

 cessive metamorphism as to be at times strongly gneissoid, and thus to 

 afford, on account of their undoubted intimate association as intruded 

 sheets in the gneisses of A, some extremely puzzling facies. The augitic 

 gneisses of series A are also troublesome as regards their relations, and 

 varieties arise about which there might be justifiable differences of opin- 

 ion in the present condition of our knowledge, but in their typical out- 

 crops all of these are easily identified and, as a broad division, the 

 classification will probably hold. After series C come the Paleozoic 

 sediments, in practically unaltered condition and representing the Pots- 

 dam of the Upper Cambrian, and the Calciferous, Chazy, Trenton, and 

 Utica of the Lower Silurian, all in fine exposures in the Champlain 

 valley.* A great series of feldspar-porphyry and basaltic dikes penetrate 



* The close parallel which the above affords with the generally accepted classification of Canada — 

 the Ottawa Gneiss, the Grenville Series, and the Norian— will be at once apparent, but the parallel 

 is not complete or at least not demonstrated in all respects, for our magnetites apparently lie in 

 the lowest of all, while in Canada they are in the Grenville. C. E. Hall, in 1879, proposed for the 

 eastern Adirondacks : T. Lower Laurentian Magnetic Iron Ore Series ; II. Laurentian Sulphur Ore 

 Series; III. Crystalline Limestones ; IV. Labrador Series or Upper Laurentian with Titaniferous 

 Ores. The relations of II and III are said to be uncertain ; but later, in a note the limestone of III 

 is said to be later than IV (32nd Annual Report of the N. Y. State Cabinet, 1879, p. 133). A full review 

 of the literature bearing on the region has been given by the writer (J. F. K.) in the Trans, of the 

 N. Y. Academy, vol. xii, 1892, p. 19, and another by Professor C. R. Van Hise in Bulletin 86, U. S. Geol. 

 Survey, p. 386. 



