246 



GEOLOGY OF THE TfflRD DISTRICT. 



iheir direction corresponds with the direction of the valley, or of the valleys by which they 

 are placed. The same observations were made conjointly with Mr. Mather in the first dis- 

 trict ; there, some scratches appejir which are of great interest from their elevation. Two 

 sets were noticed on a terrace not far below the Catskill mountain house ; one set ranging 

 with the Hudson, the other the range of the group of mountains. Another set, remarkably 

 well defined and of considerable length, is at some distance from the foot of the mountain, 

 towards the river, and ranges with the river. 



The next wood-cut, representing the well defined layers and joints of the Onondaga hme- 

 stone at Split-rock quarry, presents also a scratched surface, indicated by the oblique lines 

 which traverse it with some interruptions. The lines are in a north and south direction, and 

 in accordance with Onondaga valley. The drawing was made with a threefold object : to 

 show the well defined layers, the joints, and the scratches 



These water-worn surfaces of rocks, and their scratches more particularly, are among the 

 many interesting phenomena of geology : The first record the flow of water where none now 

 exists, and to which the smoothness of the surface in great part is owing ; and the second, 

 the sliding movement of a hard and heavy body propelled across the smoothened surface of 

 the rock. In these latter times, the scratches have attracted great attention,* and two ways of 

 accounting for them are proposed. The first is that of icebergs, which have grounded and 

 moved over the points where the scratches appear, at the time when the continent was supposed 

 to have been submerged ; the bottom of the iceberg containing fragments of hard rock, as 

 doubtless many of them must, having all been formed upon the land ; and such have actually 



