580 Surface Geology of Eastern Massachusetts. [October, 
and ten basins measured does the direction of the major diame- 
ter vary more than forty-five degrees from the general average, 
N. 5° W.; while ninety, or nearly one half the whole, deviate 
less than ten degrees from it, and only thirteen are found falling 
within ten degrees of a direction at right angles to the mean, or 
+N. 85° E. The mean ratio of the major to the minor diameters 
for these ninety ponds is 2.4; but for the thirteen it is only 2. 
The extreme range of the glacial striæ of Eastern Massachusetts, 
according to Professor Edward Hitchcock, is from N. 5° E. to N. 
55° W., —sixty degrees ; and it is found, on examination, that 
the courses of fully two thirds of the ponds lie within these 
imits 
Terntinal moraines appear to have been formed at very infre- 
quent intervals in this region ; the Elizabeth Islands, however, 
constitute a fine example of such a moraine, rendered conspicu- 
ous by its isolation; and others are known to exist inland. 
Wherever occurring, they must, of necessity, have approximately 
east and west trends, and bodies of water bordered by them will 
share the same course. In this way I conceive we may account 
for some of the extreme deviations from the mean trend ob- 
served among the lake basins. This explanation fails in many 
cases and yet these offer no special difficulty, for a more detailed 
consideration of our data shows a slight dependence of the phe- 
nomena in question on the general plan of the geologic struct- 
ure of the region. Thus, in Essex, Middlesex, Norfolk, and 
Bristol counties, and all but the southeastern part of Plymouth 
County, where the predominant strikes among the rocks are 
east and west and northeast and southwest, we find the aver- 
age relative dimensions of the ponds expressed by the number 
2.3: while in the eastern half of Worcester County, where the 
prevailing strikes range from north and south to northwest and 
southeast, that is, are generally parallel with the line of march 
of the ice-sheet, the ratio of the average length to the average 
breadth has the comparatively high value of 3.15. Hence, w° 
see that, while the lacustrine depressions are, as a nearly wni- 
versal rule, elongated in the direction of glacial movement, the 
amount of this elongation is sensibly less where the progtes® 
the ice-cap was transverse to the general strike of the underly- 
ing rocks than where it coincided with the strike. Another fact 
brought out by a comparison of these data has the same mgr 
cance, namely : the deviations from the mean trend of the basins 
are fewer and smaller where the direction of the glacial moto® 
