THE HOUSATONIC VALLEY. 783 



the west, in a very undulating course, and marked by several transverse 

 depressions, to a high isolated summit, 1 adjoining the north line of the east of 

 the North Ponds 2 (Salisbury)." (P. 129). 



In a paper read before the American Assoeiation in 1873 3 

 Professor J. D. Dana quotes Percival as stating that the mica 

 schist in which he found garnets in the township of Salisbury, is 

 below the "Stockbridge or Canaan Limestone," but giving it as 

 his own view that the schist is the overlying rock. This observa- 

 tion of Percival has considerable interest, for though the "Stock- 

 bridge or Canaan Limestone " has been shown to consist of two 

 members, one of which is below and the other above the Stauro- 

 lite-bearing rock, it is probable that Percival discovered a locality 

 at which the Riga Schist comes out from below the Egremont 

 Limestone. 



On the map accompanying Professor Dana's paper entitled 

 Taconic Rocks and Stratigraphy, 4 a number of schist areas are 

 represented within the area here treated, which he correctly 

 described to be, in some cases at least, "isolated within the lime- 

 stone area, — as isolated as islands in a sea." 5 He mentions 

 eleven of them in Salisbury and eight in the part of Sheffield 

 township just north. He believed that there is but one schist 

 horizon, which overlies the limestone, and described three local- 

 ities, nearly or quite within the area studied, to sustain his views. 

 These are, (1) the hill three miles north of Gallows Hill (locality 

 4, 1. c, p. 213) where the schist "overlies the limestone"; (2) 

 Turnip Rock (locality 5, 1. c, p. 213) where schist overlies lime- 

 stone in a shallow synclinal; and (3) Tom's Hill in Salisbury, 

 which is described as a very flat trough of schist toward the north, 

 but developing farther south into an overturned synclinal with 

 its axis dipping east (1. c, p. 214). The observations made by 



Horn's Hill. 



2 Twin Lakes. 



3 On Staurolite Crystals and Green Mountain Gneisses of the Silurian Age, by J. 

 D. Dana. Proc. A. A. A. S., 22d (Portland) Meeting, 1875, p. B25. 



4 American Journal of Science, Vol. XXIX., June, 1885. 

 s Amer. Jour. Sci., Vol. XXIX., March, 1885, p. 211. 



