Shaler.] 200 [January 19, 



If we accept the general conclusion, which it does not seem possible 

 to escape, that these drift hills are the remnants of the deposit made 

 at the melting of the great glacier, then we must believe that this 

 coating of detrital matter covered with something like uniformity the 

 whole of this part of the coast. It would necessarily vary a great 

 deal in thickness at particular points, but it should have existed 

 everywhere. If with this view we compare the structure of these 

 hills at points some miles apart, we find at once abundant evidence 

 in its support. The actual height of the summits of these drift hills 

 corresponds pretty closely. The character of the deposit is also very 

 similar indeed. The mineralogical nature of the fragments of the 

 mass may differ greatly, for in all cases a large part of the mass is 

 made up of materials which can be referred to neighboring rocks; 

 that is to rocks situated within a range of fifty miles or so; but the 

 nature of the deposit remains unchanged. Such a comparison will 

 soon exclude the possibility of these ridges being the terminal or 

 lateral moraines of a glacier, which supposition, moreover, is suffi- 

 ciently met by a mere reference to their geographical position. The 

 relation of the separate masses of drift is irreconcilable with any 

 other hypothesis than that they are the remains of what was once a 

 continuous sheet. 



The only difficulty of a serious character is to answer the question 

 which at once arises as to the cause of the peculiar parallelism of the 

 two series of ridges which are discernible in this region. The few 

 who are familiar with the geology of the environs of Boston may 

 have noticed that there are two fines of upheaval in this part of 

 Massachusetts, each marked by dykes and more or less considerable 

 dislocations of strata. One of these, and by far the most considera- 

 ble, whether measured by the frequency of the ridges or by the height 

 of the dislocations which it produces, has a course of about northwest 

 and southeast ; the other less important, but clearly marked trend, is 

 from the northeast to southwest. It will be at once observed that 

 these two systems of directions, those of the drift hills and those ob- 

 served in the series of dislocations in this district, correspond exactly. 

 With this amount of information it is by no means difficult for the 

 observer to perceive that it becomes at once probable that these drift 

 hills are only cappings of glacial detritus lying upon ridges of the 

 more solid bed rock of the country, the solid pedestal having pre- 

 vented the wearing action of the streams from affecting the detrital 

 matter which rested upon them. Wherever it is possible to get 



