80 COUESES OF STEI-ZE. 



the most striking example of this sort, is the top of Mt. Pocomptuc, nearly 1900 ft. high, 

 a few miles south of the Vermont line, in Massachusetts, where we find the rock striated 

 by a force coming from N. 30 E. Farther south, in Southampton and Granville, the 

 direction was still more towards the west, as it was in Halifax, Vermont. 



At the west, around Lake Superior, and still farther west, the evidence of a southwest 

 direction to the drift current is very striking, as shown by Foster & Whitney, and others. 

 Connecting the western examples with those in Vermont and Massachusetts, the conclu- 

 sion is plausible that a current once came up the Gulf of St. Lawrence, when the 

 country was beneath the ocean, bearing along the icebergs that striated the rocks. It 

 may be that the period of this northeast current was earlier than that from the northwest, 

 since the strise running northeast and southwest are less distinct than the others and are 



o 



seen in fewer localities. But we think further and more careful observation are necessary 

 to decide the question. 



3. FROM THE NORTH. 



These are more abundant and distinct than the other sets. They occupy the valleys 

 mostjy, and are generally rather more fresh and distinct than those upon the highest 

 mountains. We are of opinion that they were formed mainly when the ocean, then cov- 

 ering the surface, had so far subsided as to force the water into the valleys. These have 

 for the most part a nearly north and south direction, and therefore the striae, produced 

 by the icebergs which were confined within them, have the same direction. It is quite 

 clear, however, that the force which produced the striatipn, where not diverted, tended 

 southeasterly. For the average deviation in the valleys, as our Table shows, was several 

 degrees east of south ; whereas the average bend of the valleys is a little west of south ; 

 and, moreover, we find the largest quantity of detritus almost always lying on the west 

 side of the ridges. But the most decisive evidence on this point is seen in the Winooski 

 and Lamoille valleys. These run N. W. and S. E., and cross the Green Mountain range, 

 and everywhere on their bottoms and sides the striation is very distinct, while the round- 

 ed side of the ledges is the northwest side, showing without question that the grinding 

 body moved southeasterly, or up the streams. From all these facts we infer that while 

 the general tendency of the abrading force was southeasterly, the valleys turned it south- 

 erly by diverting the waters and consequently the icebergs of the retiring ocean in that 

 direction. 



The striae of the Champlain valley, as we conceive, present us with interesting examples 

 of the abrading action of ice from the remote period of the drift until the present. We 

 find not a few examples here, as the table will show, of striation from the northeast per- 

 haps the oldest of all the scratches, as we more and more incline to believe. These along 

 the lake, pointing in that direction, may have resulted from local deflection ; but more 

 probably are of the same age as the northeast system on the east side of the Green 

 Mountains. The more usual course along the lake is somewhat east of south. But on 

 the immediate shores we sometimes find an unusual variety of courses on the same sur- 

 face. Prof. Adams has noted eight at Hill's Quarry on Isle La Motte, viz., N. 3 E., 

 N. 8 E., N. 10 E., N. 25 W., N. 43 W., N. 45 W., N. 47 W., N. 65 W. On the lime- 

 stone in Shorcham, where the surface passes under the lake at low water, the stria) arc 



