Davis.] 
884 
[January 18 , 
Judd, well known from his writings on volcanoes, is a most 
enthusiastic advocate of this species ; he goes to. the extreme of 
saying that, as we can demonstrate the production of rock-basins by 
this agency in volcanic regions, and as similar though less demon- 
strable movements occur in other districts, “ are we not justified 
in accepting such movements as capable of explaining the forma- 
tion of lake-basins in all cases, rather than in having recourse to a 
purely hypothetical cause ” namely, glacial erosion ? 1 Manifestly 
we are not in the least justified in so doing ; the origin of lakes 
is so very manifold that nothing short of separate study for each 
important case will give ground for any final statement as to 
cause. As further evidence of the connection between volcanic 
action and lakes, Judd gives the following count of existing and 
extinct lakes in part of the volcanic region of Central France 
(Dept. Puy de Dome). Crater lakes clearly formed by explosion, 
18 ; lava-flow barriers, 3 ; basins among volcanic deposits or formed 
by local subsidence, 81 ; basins generally in old lines of drainage 
affected by changes of level, 174; total 276. 2 I cannot say how 
close an estimate this is, or whether, as seems probable, causes 
other than volcanic are neglected. It should be noted that it is 
as difficult to prove the subsidence of a lake-bottom as it is easy 
to suppose it ; the points where observations should be made are 
as a rule inaccessible. Scrope held the opinion that lakes in old 
craters might be due to subsidence following the eruptive period, 
or resulting from the escape of the lava below by some other vent, 3 
and if this be true, some examples given among the crater-lakes 
below should belong in this species. 
There are a few cases where the production of lakes by subsi- 
dence in volcanic regions has been almost directly observed. In 
1875 a hot lake was thus formed in the crater of Askja, the 
largest volcano of Iceland, during the progress of a neighboring 
eruption. 4 
1 Loc. cit. 11. The same volume contains in its later pages an amusing if not an 
instructive discussion excited by this suggestion. 
2 Loc. cit. 5. 
3 Volcanos, 222, 226. 
4 W. G. Lock, Roy. Geogr. Soc. Proc., in, 1881, 476; Geol. Mag., vm, 1881, 212. 
