J. F. Kemp — Great Shear-zone in the Adirondacks. 109 



and the precipitation repeated in the original solution. The 

 filtrate is transferred to a weighed platinum dish and evapo- 

 rated. Water is added before the alcohol has been expelled 

 and the evaporation continued. The residue is dissolved in 

 water. Sulphuric acid is added in slight excess. This solu- 

 tion is evaporated to dryness, the residue ignited and weighed 

 and the treatment with sulphuric acid is repeated. The resi- 

 due of insoluble chlorides may be transferred to the weighed 

 perforated crucible and dried at a temperature below their 

 melting points or it may be dissolved and the solution trans- 

 ferred to a weighed platinum dish, evaporated and the residue 

 dried, as above, and weighed. 



Chemical Laboratory, Trinity College, 

 Hartford, April, 1892. 



Aet. XY. — The Great Shear-zone near Avalanche Lake 

 in the Adirondacks ; by J. F. Kemp. 



In" July, 1889, the writer was in the region of Lake Cham- 

 plain, accompanied by Y. F. Marsters, while gathering notes 

 upon the igneous dikes so plentiful along its shores.* Our 

 attention was directed to the great trap dike which is recorded 

 near Avalanche Lake in the Adirondacks, and we made a trip 

 into the woods to examine it. Although, when viewed from a 

 distance this rock mass appeared as an undoubted dike, yet as 

 soon as it was examined in a hand specimen on the spot, it was 

 pronounced at once to be no true intrusion, but to constitute a 

 shear-zone,f or zone of wall rock, dynamically metamorphosed 

 along a fault. Subsequent microscopic examination has cor- 

 roborated this view and the case in point is an interesting and 

 somewhat unique exhibition of this phenomenon. 



Avalanche Lake, a small body of water, is the very head of 

 one of the feeders to the Hudson River. The pass by which 

 it is reached from the north is on the watershed which diverts 

 the northerly drainage into the Ausable River. The pass 

 opens directly into the Lake, which is fed by springs. It is a 

 narrow canon between vertical walls of massive rock similar to 

 the better known and larger Indian Pass farther west. It is 

 five miles into the woods from the Adirondack Lodge. On the 



* A short digest of our results has appeared in the Transactions of the New- 

 York Academy of Sciences, vol. xi, p. 13, 1891. A full account will be printed 

 elsewhere. 



fFor the use of this term compare Ch. Callaway, On the secondary minerals at 

 shear zones, in the crystalline rocks of the Malvern Hills, Quart. J. G-eol. Soc, 

 Aug. 1889. 



