Page:The Journal of geology (IA journalofgeology11893univers).pdf/382

has here a steeper hade, so that the older dolomite has been carried only a short distance over the newer beds.

Metamorphism along the fault.—Of considerable interest is the recrystallization which has taken place along the fault plane. The tremolite of the Housatonic ridge, and the large pyroxene crystals of the east base of the Cobble at South Canaan, must be explained in this way. The ragged quartzitic dolomite rock which characterizes the Housatonic ridge throughout its entire extent and is not found elsewhere in the region, is believed to owe its characters to a crushing along the fault and a recementing of the fragments by a vein quartz—it is in other words, a fault breccia.

In the vicinity of the great thrust planes of the Northwest Highlands of Scotland, which have been so carefully studied by Geikie, Peach and Horne, and their associates of the Geological Survey of Scotland^[1], schistose structure and new minerals have been developed by the shearing, micas, hornblende, actinolite and garnet being produced in this way^[2]. Another instance of this sort is furnished by the overthrusts of the Rocky Mountains along the line of the Northern Pacific Railway.^[3] These thrusts have likewise produced metamorphism of the beds along the thrust planes, argillaceous layers being made schistose and limestones being whitened and cracked.

Thickness of the Egremont Limestone.—In the Mt. Washington paper, I have shown that the thickness of the Egremont Limestone in the southern portion of the summit plain is less than one hundred feet, and that a little farther south it probably dies out altogether. In the northern portions of that area, where it