90 Reports and Proceedings— 
able for the work of erosion; most of the energy is expended wethin 
the mass of the glacier in overcoming cohesion. 
3. If the ice, though flowing really in a way comparable to the 
motion of a river-current (the upper layers moving faster than the 
lower, the median portions faster than the lateral), retained its con- 
tinuity, the strain against the rocks might be great enough to do much 
that is required of it by the ‘‘erosion-theory ;”’ but here comes in the 
remarkable absence of ductility of ice, giving birth to crevasses, the 
varieties of which are all referable to one common principle, and 
adverse to erosion. 
4. Prof. Tyndall was quoted as an authority for the fact that there 
is a gradual transfer of ice-particles from the bed towards the surface 
of the glacier, a fact which the author attempted to explain later on 
in the paper by reasoning adopted from Helmholtz. The fact itself is 
directly opposed to erosive action. 
5. The instance of the Morteratsch glacier was more particularly 
considered; and an attempt was made to show that the assumptions 
which underlie the reasoning by which Professor Tyndall has endea- 
voured to meet the objections which have been raised to the erosion- 
theory from observations of the Morteratsch, are incompatible with 
sound mechanical principles. 
6. The important law of the lowering of the freezing-point of water 
by pressure was next discussed, and reasoning adopted from Helmholtz, 
which leads to the remarkable conclusion that within the glacier water 
at 0° C. exists in contact with ice below 0° C. This was accepted by 
the author as the explanation of the otherwise unintelligible fact 
referred to in 4. 
7. The last point led to the discussion of Dr. Croll’s views on 
glacier-movement. The author gave reasons for rejecting Dr. Croll’s 
so-called ‘‘ molecular theory”? of the movement of glaciers (it is really 
little more than a restatement of the regelation theory disguised by 
a misuse of the terms “molecule”? and ‘‘molecular’’), and for not 
sharing his feeling of ‘‘mystery’” about the theory of regelation. 
8. A real work of erosion was shown to go on in connexion with 
glaciers, by the direct action of the glacier-streams; but the same 
objections apply to these as to streams flowing in an open valley, as 
agents capable of excavating basin-like hollows. 
9. The remainder of the paper was mainly occupied with a con- 
sideration of “tarns”? among the mountains. Here it was admitted 
that a glacier may work in a different manner from a glacier moving 
down a valley; and so it was thought many small rock-basins (now 
tarns) may have been formed at the toot of precipices. On the other 
hand, it was maintained that many tarns occupy hollows formed by 
earth-movements on the mountain-slopes, or by moraines. 
10. In conclusion, the author strengthened his position by pointing 
to the rejection of the erosion-theory by such high authorities as 
Professors Bonney, Helmholtz, and Credner, and Mr. John Ball; and 
expressed his regret at finding himself at issue with Sir A. Ramsay, to 
whose geological writings we all owe so much. 
Generally, the author concluded, from mechanical and physical 
considerations, that far too much erosive power has been attributed by 
