THE HOUSATONIC VALLEY. 793 



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 crys- 

 tals 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 east- 

 ward did not seem to be separated from the pyroxene-free lime- 

 stone 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 pro- 

 nounced, 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 else- 

 where in the region. It is a dolomite abounding in tremolite 

 and containing layers of quartzite and quartzitic dolomite. Par- 



1 The southern portion of this ridge (that east of the river) is the ridge mentioned 

 as Canaanite on page 126 of Percival's report. 



