ESSEX COUNTY. 
215 
59 . 
Great Trap Dyke at Avalanche Lake. 
Mount McMartin, which rises boldly from Avalanche lake, is nearly bisected by an enor¬ 
mous dyke. The mountain may be seen from the outlet of Lake Henderson at Adirondack, 
bearing N. 67° E. Its distance is between live and six miles by the common route, as esti¬ 
mated by hunters who are familiar with the ground. Comparing its elevation with Mount 
Marcy and others in this group which have been measured, its height cannot be much less 
than live thousand feet. 
The dyke, which is the most remarkable object at this place, cuts through the mountain 
nearly from top to bottom. At its base, where it rises up from Avalanche lake, a deep gorge 
has been formed by the action of a small stream, which rises some distance up the present 
gorge, probably in several small springs. Its depth is about one hundred feet, and it is 
bounded by perpendicular walls of naked rock, with numerous clefts, however, which permit 
