515 
the following are important desiderata. With respect to elongated 
ridges and tumuli of gravel, it remains to discriminate how far they 
may have been derived from, or modified by, the action of ice under 
one or more of the three following conditions: 1. Were they lodged 
by glaciers alone, without the agency of water, in the form of mo- 
rains on their flanks and front? 2. Have they been stranded by 
icebergs loaded with gravel upon the shores of lakes, or estuaries, 
or seas? 3. Have they been dropped in deep water by floating and 
melting icebergs, and re-arranged by whirlpools and conflicting cur- 
rents in the form of oblong reefs and groups of obtuse cones which 
they actually present? Another large field of inquiry must be 
forthwith entered upon, in the distinctions we shall have to make 
between raised sea-beaches and: each of the three last-named resi- 
duary effects of glacial action. 
With respect to scorings also and dressings on the ‘surfaces of 
rocks, it is very desirable that we should find some criterion where- 
by to distinguish between the grinding effects of glaciers marching 
slowly along dry land, and of icebergs dredging the bottom of the 
sea, and of large stones and gravel drifted simply by water, in pro- 
ducing strie, grooves and furrows, together with rounded and po- 
lished surfaces on the rocks over which they respectively advance. 
I see not yet by what test we may distinguish these residuary 
phenomena where they occur in regions now remote from either of 
the causes most competent to their production, viz. in countries that 
now enjoy a temperate climate and are in some cases elevated nearly 
four thousand feet above the level of the sea; for where the sup- 
posed agent is ice armed and transfixed with stones projecting like 
the teeth of a file from its base and sides, the effects of similar in- 
struments on similar materials would probably be the same, by what- | 
ever cause a slow progressive motion may have been imparted to 
them; and whether on dry land or beneath the sea. 
It remains, moreover, to ascertain to what extent the sudden 
elevations of land may have-produced great movements of water 
and diluvial inundations by gigantic waves, analogous to those 
which are occasioned by modern submarine volcanic action ; and to 
inquire into the effects that may have been produced on the sides 
and bottoms of valleys of denudation by the driftimg of the hard — 
materials that must have been swept through them at and after the 
time of their excavation. 
- A further subject of inquiry is, whether there be parallel striz and 
furrows on the truncated and abraded surfaces of older rocks that 
haye been overlaid by more recent strata, after an interval in which 
these surfaces had been exposed to the action of the sea. In cases 
of this kind that have come under my observation, the surfaces have . 
only been cut off transversely and ground smooth, like the shores 
of the present seas; but they have no such parallel strize as those 
which are of general occurrence beneath diluvium or drift*; nor 
* They are sometimes also perforated by lithodomcus molluscs, and other- 
wise beset with parasites, which indicate a period of tranquillity between the 
action of the forces by which they were shorn away or made smooth, and 
the deposition of the stratum that was subsequently formed over them. 
