RlES GrEOLOGT. OF ORANGE Col X I V. 



445 



limestone crops out on the same road to the south of the slate, as well as 

 on the opposite side of the ice pond. The fault between the gneiss and 

 limestone on the west side of the hill seems to pass to the north between 

 the latter and the slate, or may die out. 



The gneiss of both Cronomer's hill and Snake hill is a granular mixture 

 of quartz and feldspar, with little or no mica. In a small gneiss area south 

 of Snake hill the rock is often graphitic. 



The Hudson river slates extend to the foot of the mountain between 

 Mountainville and Cornwall, and are possibly faulted against the gneisses of 

 the Highlands. The two can be seen close together at several points about 

 one mile and a half south by east of Canterbury, the slate apparently dipping 

 under the gneisses (420). The gneiss strikes N. 30 c> E., and dips southeast. 



One-half mile south of Cornwall (421) is an old road-metal quarry in 

 limestone. It is a dark grey, finely crystalline rock, striking N. 80° E., and 

 dipping 45° S. There are interbedded grey brown, siliceous layers, and 

 numerous black patches of carbonaceous matter along the bedding planes. 



The limestone passes under the slates and probably belongs to the 

 Olenellus quartzite, certain members of which it resembles very closely. 

 About twenty-five feet of limestone are exposed (422). The dipping of the 

 quartzite against the Pre-cambrian gneiss would at first suggest a fault, 

 but it may be the southern side of a fold caused by the quartzite being thrust 

 against the gneiss. This, Professor D wight informs me, is sometimes the case 

 in Dutchess county. The slate and gneiss are seen almost in contact a few 

 feet east of the quarry. 



The writer mentioned this limestone quarry to Professor D wight, who 

 has done much field work in the neighboring counties, and he has written in 

 reply: "In 1883, I found that there is a thin stratum of impure, hard lime- 

 stone overlying the gneiss, and underlying the Hudson river shale along 

 the northern and northeastern base of Storm King and south of Cornwall. 



" This occurs, as I then ascertained and noted, on the estate of Mr. S. B. 

 Young, whose house is at the northeastern base of the mountain, south of 

 Corn-wall. This stratum of limestone was encountered in making excavations 

 for the cellar of his house, and for his ice-house. Blocks of the excavated 

 limestone lie around, and some of them were built into the walls forming the 

 approach to the ice-house." 



Further on in his letter, Professor Dwight says, in referring to the 

 quarry: "I take the limestone in question at Cornwall to be the Lower 

 Cambrian limestone (Olenellus horizon).'" 



