Page:The Journal of geology (IA journalofgeology11893univers).pdf/377

underlying schist through a slight fault. The marked difference between the sections north and south of the track is due to steep southerly pitch.

The great Housatonic Fault.—Enough has been presented in the Mt. Washington paper and in the present discussion, to show that the limestone of this region is divisible into two horizons—the Canaan Limestone or Dolomite, lower than the Riga Schist, and the Egremont Limestone above that schist. Additional evidence might be brought forward, if it were necessary, from the region lying to the southward in the vicinity of Limerock. As has also been stated, the Canaan Dolomite, particularly in the vicinity of Canaan and in the valleys east and northeast of there (Monterey, Mill River, Clayton, East Canaan), abounds in crystals of white pyroxene, which has never as yet been found in the Egremont Limestone. Hence this mineral has a certain value for purposes of identification, comparable with that of the garnet and staurolite of the Riga Schist. Masses of Canaanite also occur in it though absent from the Egremont Limestone. Early in this investigation, when the possibility of a differentiation of the limestone was only suspected, this lithological peculiarity was noted, but as the pyroxene-bearing limestone to the eastward did not seem to be separated from the pyroxene-free limestone to the westward by any areal break, the question of divisibility was left open. It was, however, observed that the Housatonic river roughly outlined the westward extension of the pyroxene-Canaanite rock to the north of the interstate boundary. Another striking feature of this line is a ridge more or less pronounced, having its course along the banks of the river. In the southern half it follows the east bank of the river, but crosses it at the small hill called the "Cobble," just northeast of Miles Hill, and to the north of that point borders the west bank.^[1] This ridge is composed of a rock which has not been found elsewhere in the region. It is a dolomite abounding in tremolite and containing layers of quartzite and quartzitic dolomite. Par-