TWO SETS. 



81 



very fine and vary considerably in direction, in a few cases as much as 90. Some of the 

 striae in such cases are also very fresh, and we can easily believe that some of them may 

 have been made by the expansion of the ice of the present lake, which along the shore 

 may have pebbles frozen into it, and when subsequently crowded eastward from the cen- 

 tre of the lake, or lengthwise of the same by the wind, striation may have been the result. 

 If so, this work may have been going on from the time when huge icebergs were borne 

 southerly by the ocean, when it extended from the Glulf of St. Lawrence to the bay of 

 New York, when most of New England, as well as Essex county, N. Y., was an island, 

 or group of islands, and the direction of the currents and the icefloes was modified by the 

 projecting ridges. As the water decreased the friths would gradually change into lakes, 

 and the icefloes and icebergs into fixed sheets of ice, which, in the spring, might be lifted 

 up and moved southerly by the current, leaving traces of its movement on the abraded 

 rocks. Thus the present strise may be the resultant of all that have been made from the 

 drift period to the present time. 



The same reasoning will apply, mutatis mutandis, to the strise in the Connecticut valley, 

 which for the most part have the same direction, with a southeasterly tendency, and which 

 are seen in some cases passing beneath the water at 

 its lowest mark. Very likely some of these may 

 have been produced by ice floods at a modern period 

 in the history of the river. Yet in general the dis- 

 tinction between river action and drift action, is 

 very obvious as, for instance, at Bellows Falls. 



In Halifax, which in the central part is almost 

 as high as the Green Mountains, drift strise are 

 unusually distinct and abundant. Here we have 

 at least two directions on the same limited surface, 

 as is shown on Fig. 29, sketched from a rock a 

 few feet in diameter, about two miles northeast of 

 the centre. 



A. D. Hager has furnished an interesting sketch from a stereoscopic view of some 

 bowlders, and the striae made by them, on Mansfield Mountain. (Fig. 30.) 



FIG. 30. 



FIG. 29. 



