72 Rev. J. F. Blake — Form of Sedimentary Deposits. 



Far different is the power of a tilt transverse to the stream-line. 

 This will make one side of the valley more steep, the other less, 

 and may thus go on to some extent without destroying the water- 

 flow. But so soon as the angle of tilt exceeds the slope of the 

 opposite valley-side, that slope becomes reversed ; instead of 

 shedding water down to the river-bed, it drains water away from it, 

 and the valley is a valley no more. Its place in the scenery of the 

 country is now taken by a feature which shows as a steeper slope 

 with a gentler slope below : in profile like a cliff above a talus, or 

 a river wall running along a river beach. But since a valley is 

 rarely a straight trench, and a tilt can seldom be uniform, different 

 parts will suffer in different degrees, so that traces of the trench 

 may frequently remain. Those valleys will suffer most which are 

 most nearly strike-valleys to the dip of the tilt. I suppose it has 

 been already pointed out somewhere that, in a sinuous valley, the 

 first effect of a tilt transverse to its general direction will be the 

 creation of lakes on the lower sides of its windings. 



I conclude, then, that the agents most able to efface a river valley 

 are those which change the inclinations of strata ; and that even 

 these agents may effect considerable alteration in the surface 

 without effecting a valley's destruction. But a powerful and 

 incessant enemy is the river itself. For this in its sinuous lower 

 course is ever tending to widen its trough, that is, to make the 

 valley a less conspicuous feature of the relief. The valley opens 

 out into an estuary ; the estuary into a gulf, perhaps a sea. 



' Permanence ' does not precisely express the property which has 

 here been discussed. This somewhat resembles a power of 

 recovery from disaster, of awakening from hybernation or from 

 sleep ; an animal's reproduction of a lost limb ; the regrowth of 

 a broken crystal restoring its form. The valley shape may be lost 

 for a while, but there remains a possibility of its restoration. We 

 might almost talk of its vitality. 



The valley retains its vitality, though its own river be burying 

 it with sediment. Such sediment comes from the ridges between 

 channels ; the channels may be filling up while the ridges are 

 being worn down, but if the channels are being cut, so also in 

 general the ridges. Thus ridges may be the localities of more 

 continuous degradation, and of irreparable destruction. 



In view of this inherent vitality we may well believe some present 

 valleys to be extremely ancient features of our earth's surface. 



VI. — On the Original Form of Sedimentary Deposits.^ 

 By the Eey. J. F. Blake, M.A., F.G.S. 



{Concluded from the January Number, p. 18.) 



WE may now examine how far these theoretical conclusions 

 explain and are confirmed by what is seen in nature. First 

 we know that in most formations there are great masses of what is 

 now, or must have been once, fine-grained sediment. These often 

 1 A paper read at the Meeting of the British Association, Belfast, September, 1902. 



