NATURAL HISTORY AND PHYSIOGRAPHY OF NEW BRUNSWICK. 53 



Falls in glaciated regions are chiefly the result of the damming 

 or filling of shallow valleys by glacial drift dropped across them at the 

 close of the Glacial Period, by which the water was held back and 

 made to seek an outlet over the lowest point of the rim of the valley, 

 which usually is a rocky ledge. Such dams are easily to be seen at 

 the falls on these western rivers. On the other hand, where long 

 stretches of rapids or of even descents over ledge-rock occur, the river 

 is probably in its pre-glacial channel ; and pre-glacial channels usually 

 have no falls, other than small ones due to unequal hardness or jointing 

 of the rock, and hence to uneven erosion, because there was ample 

 time in the pre-glacial ages for any which may have existed to have 

 become eroded out, as all falls are tending to do. In general, then, we 

 may conclude that where falls and dead waters are, the pre-glacial 

 valleys are more or less filled up, while long series of rapids over ledge- 

 rock, as a rule, indicate a pre-glacial channel. Now, while the western 

 series of our rivers have large portion.! of their valleys of the dammed-up 

 sort, those of the eastern series show no glacial dams, and no glacial 

 falls — at least in their lower courses ; but the channel is always of 

 bed rock, except where thinly covered by gravel and boulders, brought 

 down by the stream itself. But why were these eastern valleys not 

 also dammed by the glacial drift 1 Was the region not glaciated 1 

 Now there is abundant evidence that it was, though probably not so 

 heavily as the less elevated western section. But while the quantity 

 of drift dropped in Southern New Brunswick was sufficient to fill the 

 comparatively shallow valleys of the western series, it could not fill to 

 the tops these eastern valleys of 400 to 500 feet of depth, and, unless 

 they were filled completely to the top, and a little more, the rivers 

 would not be forced out of them, and hence would form neither new 

 falls nor new valleys, but would simply cut out and wash away the 

 glacial dam itself and resume their pre-glacial beds. The depth of these 

 valleys, then, if this explanation be correct, has been their salvation, 

 and the different depths of the valleys in the two series is the real 

 reason for the presence of the falls at the mouth of the one series, and 

 their absence from the other.* 



* The same general explanation will no doubt also apply to some other deep valleys, 

 such as that of the Restigouche, which has no falls, but everywhere a rocky channel. 



Dr. G. F. Matthew, in remarks made after the reading of this paper, suggested, as 

 subordinate influences at work to aid in producing the differences between the two series, 

 the following: First, the high eastern plateau tended to turn aside the glacial currents 

 into the St, John, and hence less drift was dropped into the eastern than into the western 

 series, which have valleys directly along the line of the glacial flow. Second, the much 

 greater slope of the eastern rivers must have given them greater power to wash out drift. 

 Third, the formation through which the eastern series have cut their valleys is fairly uniform 



