EQUIVALENCY. 341 



" It is a remarkable fact that the Hudson River slates do not appear between the Tren- 

 ton limestone at Highgate Springs, and the Oneida grit (red sandrock) at Saxe's Mills, 

 two or three miles east; while still further east, where the grits have been worn through, 

 the slates appear beneath, decidedly unconfonnable. Fig. 247 illustrates this position. 



Fia. 247. E Explanation of Fig. 247. 



A Clay slate, dip 67 W., strike N. 15 E. 

 B Coarse limestone (red sandrock), dip west. 



Jk /1/?>W C -A -^L ""* I C Debris from D and E. 



ir&n I m-n*m- 



D Gray sandstone (red sandrock), dip 5 E. 

 Section in Highgate. E Coarse limestone (red sandrock), dip 5 E. 



The slate, A, lies in a valley between two hills of red sandrock, and it shows itself in two 

 or three places. The ledges of sandstone and limestone, D and E, are thirty feet long, 

 and the sketch is taken from ledges on the telegraph road in Highgate, one mile west of 

 Mr. Haflin's stone house. The evidence in favor of the unconformable position of these 

 rocks is not so clear as we could wish, yet it seems to agree with the position of things at 

 Highgate Falls, two or three miles south. 



" Do not these facts show that after the slates had been formed and elevated at a small 

 angle, the Oneida Group was deposited upon their edges, entirely concealing both the 

 Utica and Hudson River slates east of Highgate Springs ? and that in the alluvial period 

 the Oneida grit was worn through at the locality of Fig. 247, thereby revealing the slates ? 

 The slates also appear to the east of the grits [Georgia slate.] 



" Two additional facts confirm this view : 



" 1. The Oneida grits at Highgate Falls occupy a depression in the slates. There seems 

 to be a depression like a trough, excavated from the edges of the slates, in which the grits 

 were subsequently deposited. It is unusual for the slates elsewhere to occupy the higher 

 place, because they decompose more readily than the tough sandstones and breccias. The 

 higher position of the slates may be seen upon the north branch of the Missisco River, 

 not a great distance from the village of Highgate Falls. 



" 2. The elevation of the slates was caused by the formation of the great anticlinal 

 axis which separates the eastern and western Palaeozoic barriers of North America from 

 each other. This elevation probably took place near the close of the Hudson River 

 period. As the lower silurian limestones experienced great lateral pressure during this 

 disturbance, they were plicated (as is shown in the Trenton limestones at Highgate 

 Springs, in Fig. 181.) The same force must have affected the slates overlying the lime- 

 stones, though they may not have been so much disturbed. They might simply be tilted 

 up at a small angle, so that the rock next formed would rest upon its edges discordantly. 



" If this unconformability be admitted, it simply adds to our previous knowledge, the 

 fact of the existence of discordant stratification between the Hudson River Group and the 

 upper silurian in a new locality. The Canada geologists have described a similar uncon- 

 formability of these same rocks as they extend to Gaspe, near the mouth of the River St. 

 Lawrence. 



" Following the grits and slates southerly in Vermont, the greater inclination of the 

 Hudson River slates than the overlying sandstones is nearly constant. For instance, at 



