Davis.] 
828 
[January 18, 
the source of the Shannon, is described by Hull, 1 as an old valley 
interrupted by an up-throw fault, probably of late Tertiary date ; 
the barrier has been much worn down, but not yet entirely 
destroyed. The Dead Sea occupies a depression, apparently the 
result of a down-throw fault of considerable length, north and 
south 2 ; the northern of the two narrow bays in which the Red Sea 
ends is in the prolongation of the same line, and very probably 
connected with it. Whether the Dead Sea derived its salt from a 
former connection with the Red Sea or from its inflowing streams 
is a question that has been much discussed, but is apart from our 
present consideration. 
Desor’s division of orographic lakes 8 includes some basins that 
will here be described under other headings. His Mulden-seen 
(trough or synclinal lakes) generally come under our second species, 
but his Combe-seen (hollows on the eroded surface of a soft stra- 
tum between two parallel ridges, i. e., in a longitudinal monoclinal 
valley) and his Cluse-seen (in cross valleys) need some further 
examination. The combes , if produced by ordinary erosion, cannot 
contain basins unless their valley line is interrupted by a deposit 
barrier, and then they fall under our class of obstruction lakes. 
The cluses which he seems to attribute to an actual splitting 
open of a cleft across the mountains, should be considered the 
result of erosion like the combes, and as such can as little have 
any basin form ; basins in cross-valleys must be due to some- 
thing more than simple water erosion (see Warped Valleys, p. 
330, Delta-fan and Moraine Barriers, C. 1 and 3). Riitimeyer well 
criticises this grouping as amounting to nothing more than say- 
ing that the rock structure is the same above and below water 
level 4 ; except for the trough basins, it certainly gives no sufficient 
explanation of the origin of the lakes so classed. The altogether 
impossible lakes represented in Desor’s figures, which we are sur- 
prised to find imitated by Reclus andPeschel, might indeed be the 
1 Phys. Geol. and Geog. of Ireland, 1872. 189. 
2 L. Lartet, Note sur la formation du bassin de la Mer Morte Soc. Gdol. 
Bull., xxn, 1865. 420. Peschel, Phys. Erdk., n. 325. 
3 Desor, De la physiognomie des Lacs Suisses. Revue Suisse, 1860. Deutung der 
Alpen-Seen, in Gebirgsbau der Alpen, Wiesbaden, 1865. 
4 Op. cit. 50, note. 
