162 
Reconh of the Geoloijicai Surrey if India. 
[vOL. XIII. 
the case fairly, not to say strongly, made out as regards some, and capable 
of being extended by analogy, and in default of any sufficient reason to the 
contrary, to all. 
Mr. Ball (p. 176 /. r.) commences by dividing the Kumann lakes into three 
classes “ having certain features mutually in common,” but unfortunately without 
specifying what these features are; an omission which must be my excuse if 
I fail in consequence to do justice to my colleague’s views on the subject. 
Passing to the consideration of Naini Tal (of which a pretty lithographed 
sketch is given) Mr. Ball seeks to controvert the views of those who attri¬ 
bute a glacial origin to its basin, but quite unsuccessfully, I think. Whether 
this lake really lies in a tx'uo ice-cut basin or basins, is certainly not established 
or likely to bo so by actual jrroof, unless the lake is ever drained, a contingency 
which may be dismissed from present consideration, though if Mr. Ball’s section 
of its basin represents the general contour of its bottom, and not the contour 
along a single line only, there is the strongest presumption in favour of its gla¬ 
cial origin. I do not, however, think it neces.sary now to dwell at any length 
on Mr. Ball’s speculations as to the probable nature of the bottom, but there is 
one I'cmark of my colleague touching the mode in which the rock basins (sup¬ 
posing them to exist) have been pi'odueed, which indicates so absolute a diver¬ 
gence from the current ideas respecting the modus operandi of ice action, that 
I do not like to pass it without remark. Mr. Ball’s words arc (p. 176 I. c.) “ sup¬ 
posing it to be so, the twin basins might be readily explained by the hypothesis 
that they had been successively excavated by the retreating end of a glacier.” 
This is perfectly unambiguous as far as language goes, but does Mr. Ball really 
suppose that a glacier ever moves backwards, and if not, then what does he 
mean by the above words ? 
A glacier does its work by its weight and momentum; its movement is sole¬ 
ly forwards, not necessarily downwards, but simply forwards, and away from the 
direction of its source. The “ retreating end ” of a glacier, therefore, cannot 
excavate in any degree, or add in its I'ctreat, to the work it had already per¬ 
formed in its advance; since the word “ retreat ” does not involve here any sense 
of rctrui/nuh motion, but simply a contraction of the dimensions of the glacier 
induced by the operation of climatal causes. As the end of a jet of water retreats 
as the pressure under which the jet issues is diminished, without, however, 
the particles which compose the jet losing their forward motion (though its 
amount may bo reduced), so it is with a glacier, and I am therefore at a loss to 
know Avhether, in the passage cpioted, my colleague’s words correctly express his 
meaning.^ 
I do not consider either that Mr. Ball has been particularly felicitous in his 
cfl’orts to dispose of the argument adduced by Mr, H. B. Blanford for the glacial 
origin of the lake, frxxm the peculiar sluipe of the basin, and the character of its 
sides, unbroken by subordinate ridges and spurs. 
' Mr. Biill uuiy pcrhiips be creditoil witli tbo nioiuiing liis worck would suggest to most of bis 
rcndoi's—tliat. tlie upper biisin hud been cut alter the gUieier bad retreated trom its position ol 
nia.ximum exteusion.—II. B. M. 
