1882 .] 
34T 
[Davis. 
« 
The evidence in favor of the origin of these Maare by violent 
eruption is : 1°, finding that a series of transitional forms exists 
between true Maare and accepted craters of eruption, which are 
mostly common in their neighborhood; 2°, the occurrence some- 
times observed of fragments of the non-volcanic rocks in which 
the basins are hollowed out, among the neighboring volcanic ejecta ; 
3°, the known violence of certain volcanic eruptions above noted. 
On the other hand, there are cases that should better be explained 
by local subsidence, probably connected in some way with the 
neighboring volcanic eruptions because 1°, no trace of ejected 
material can be found ; 2°, so far as the non-volcanic rock in which 
the basin is excavated can be seen, it does not show any marks of 
eruption. 1 
A peculiar example is Lake Lonar, on the trap plateau of the 
Deccan ; a shallow salt pool at the bottom of a cavity about a 
mile in diameter and three or four hundred feet deep : on the 
north and north-east sides, the edge of the hollow is on a level 
with the surrounding country; elsewhere there is a rim of blocks 
of trap forty to one hundred feet high. The volume of the rim, 
however, is only about a thousandth part of the cavity; and no 
lava flow from it can be detected on the surrounding surface. 2 
Similar basins are found in the Azores 3 and in Central Amer- 
ica and Mexico. 4 
C. Obstruction Basins may be separated into two families : 
in the first, a valley or trough, produced by constructive or destruc- 
tive forces, receives a local deposit that serves as a barrier, and so 
completes the basin ; in the second, a basin remains .on the sur- 
face of a deposit, because of a lack of material to fill it, or because 
the irregular distribution of sediments fails to bring all points to 
the same level. These may be called Barrier and Enclosure Basins 
and are further divisible as follows. 
vulkanische Seen in der Auvergne, Neues Jahrb., 1870, 460. This author is inclined 
to regard these lakes as the result of subsidence. See our page 385. 
E. Vimont, Les lacs Pavin, de la Montsinevre et de la Godivelle, Club Alpin Frain?. 
Ann., i, 1874, 337-349. The second named is a lava-barrier basin; the third, an ordi- 
nary crater of eruption. 
1 A. v. Lasaulx, Niederrhein Ges Sitz’b., xxv, 1868, 67. 
2 Medlicott and Blanford, Geol. of India, 1880, i, 379. 
* Hartung, Die Azoren, Leipzig, 1860, 312. There known as “ Caldeiras.” 
4 Squier, Mexico, 1850, 270. 
