60 SURFACE GEOLOGY. 



I have been finally led to adopt, as to the formation of moraine terraces. I regard 

 them as mainly deposits by water, urged in currents through the sinuosities of 

 stranded icebergs. The subsequent melting of the ice, as the surface was drained, 

 would leave it with those convolutions and anfractuosities, so like those upon the 

 human brain. That powerful currents occur among stranded icebergs, we have 

 the testimony of Sir James Ross, who " mentions that the streams of tide were so 

 strong amid grounded icebergs at the south Shetlands, that eddies were produced 

 behind them; so that as far as such streams were concerned, they acted as rocks. 

 Navigators have observed icebergs sufficiently long aground in some situations, 

 that even mineral matter might be accumulated at their bases in favorable situa- 

 tions, while tide currents may run so strongly between others, that channels 

 might be cut by them in bottoms sufficiently yielding, and at depths where the 

 friction of these streams would be experienced. Much modification of sea bottoms 

 might thus be produced by grounded icebergs, &c." (De la Beche's Geological 

 Observe?; p. 254.) 



Such masses of ice are liable, at some seasons of the year, to be crowded forward 

 by other ice, so as to plough furrows in the loose materials, and grind down and 

 striate the rocks in place. Sir Charles lyell quotes an interesting case, in which 

 mounds analogous to moraine terraces were produced "by the pressure of ice." 

 From the account given by Messrs. Dease and Simpson, of their recent Arctic 

 discoveries, we learn, that in lat. 71° N. long. 156° W., they found "a long low 

 spit, named Point Barrow, composed of gravel and coarse sand, in some parts more 

 than a quarter of a mile broad, which the pressure of the ice had forced up into 

 numerous mounds, that viewed from a distance assumed the appearance of large 

 boulder rocks." (Lyell's Principles of Geology, p. 230.) 



Such statements, especially the last one, give great plausibility to the theory 

 which I have adopted. It is still further strengthened by the fact, that these 

 moraine terraces occur in spots, which must have been the shores of the ocean, 

 or of estuaries, or of lakes, as the waters were retiring; and, therefore, just the 

 spots where icebergs might be expected to get stranded. They are found, also, as 

 a part of the earlier terraces, not long posterior to the drift, while as yet we may 

 presume the temperature was low enough to allow of the long continued presence 

 of ice along the shores. 



But though the preceding views may explain the rounded hillocks and inter- 

 vening depressions of the moraine terraces, something more seems necessary to 

 account for those remarkable ridges of sand and gravel, usually more or less ser- 

 pentine, that accompany the mounds in some instances, as at Andover. Now in 

 high latitudes the shores are found sometimes to be composed of layers of sand, 

 gravel, and ice, more or less interstratified ; that is, the waters throw up gravel 

 and sand upon and among the ice along the shores. As the ice melts away, we 

 might expect ridges of sand and gravel to remain, being crooked or straight as the 

 shores were. It seems to me that this may have been the origin of such ridges of 

 this kind, as have fallen under my observation, the most striking of which are in 

 Andover, Mass. 



I have seldom been so much perplexed to find a name for any natural object as 



