1882 .] 
333 
[Davis. 
years. 1 Lake St. Mary is the largest of these submerged tracts, 
now measuring thirty miles in length by five to seven in width. 2 
In India, at the mouth of the Indus, a much larger surface was 
submerged by the earthquakes of 1819, and a shallow sea, two 
thousand square miles in area, is the result. 3 During the great 
Calabrian earthquake of 1783 the Lago del Tolfilo, 1700, 900, and 
50 feet, in its three dimensions, is said to have been formed sud- 
denly by the opening of a great chasm, and filled by water issuing 
from its bottom. 
Lakes formed by land-slips during earthquakes will be noticed 
farther on. 
A. 6. Volcanic Subsidence Basins. Depressions found in some 
volcanic regions are ascribed to the settling down of the surface 
rocks into cavities emptied by the ejection of lava, but the con- 
nection between cause and effect is seldom closely demonstrable. 
Lake Balaton (Flatten See) in Hungary, fifty miles long, three 
to ten wide, and forty feet deep, is given as an example of this 
species, as its longer axis is parallel to a line of local volcanic 
action. 4 Lake Tuapo, in New Zealand, is probably of the same 
origin ; it is a depression in volcanic rocks, twenty by twenty- 
five miles in cross measure, and is bordered by modern cones of 
eruption ; Lake Rotorua is referred to the same cause. 5 The old 
supposition of the existence of volcanic rocks in the Thian Shan 
Range has recently been confirmed, and the Chaderkul near by is 
explained as an area of subsidence following their eruption. 6 
Lough Neagh, in northeastern Ireland, probably belongs here; 
it is a broad, shallow depression in a region of faulted volcanic 
rocks and is of preglacial origin. 7 Some of the larger circular lakes, 
Bolsena, Bracciano, and others of Central Italy, may be of the 
same origin. 8 
1 Lyell, Principles of Geology, n, 108. 
2 Humphreys and Abbott, Report on the Mississippi River, plate n. 
3 Frere, Geograph. Soc. Journ., xl, 1870, 181. 
4 Judd, Geol. Mag., in, 1876, 6. 
5 Hochstetter, New Zealand, 1867, 365, 370 ; Reise der Novara, i, 1864, 144. 
6 Stoliczka, Geol. Soc. Journ., xxx, 1874, 574. 
7 Hardman, On the Age and Mode of Formation of Lough Neagh, Ireland Geol. Soc. 
Journ., iv, 170 ; and Hull, Phys. Geol. and Geogr. of Ireland, 1878, 186. 
8 G. Vom Rath, Die Umgebungen des Bolsener Sees. Deutsch. Geol. Ges. Zft., xx> 
1868, 265. 
