Davis.] 
326 
[January 18 , 
ful from the rainy mountain slopes, and their evaporation being 
restricted by the decreased ratio of surface to volume. 
We can give no simple examples of this species ; for as erosion 
and deposition both go on and probably with accelerated rate 
during the progress of mountain making, the enclosing ridges will 
be worn down as they rise, and their waste transferred to the 
nearest subsiding trough, and it will be rare to find a basin pre- 
serving its simple orographic form. Moreover, an excess of 
deposit thrown into the trough at the confluence of a lateral with 
the main valley frequently forms a barrier and holds the lake 
higher than it would otherwise stand, so that it becomes a hybrid. 
Baikal, Issikul, 1 and Nicaragua so far as they are known, come 
under this species. 
The western part of Lake Superior has a basin of this kind 2 ; 
but the others of our Great Lakes cannot be attributed to an oro- 
graphic origin, and they all owe part of their water to obstructed 
outlets (see C. 4). Nyassa and Tanganyika come perhaps as near 
this species as the first ; they are decidedly elongated, and consid- 
erable mountain ranges rise in their neighborhood. Titicaca is 
presumably another intermediate form; although smaller and 
lower than it has lately been it is still nine hundred feet deep and 
preserves its outlet and remains fresh ; Lake Aullagas, into which 
its Desaguadero empties, is shallow and brackish, and the sink 
into which this is drained is decidedly salt. The remains of 
many similar old lakes now appear as pampas on the Plateau of 
the Andes. 3 Although mentioned here, they probably belong 
partly under the Fan Delta and New Land species. 
The southern part of the Caspian owes its depth to a pronounced 
orographic origin. So in the Himalaya, the valleys of Nepal and 
Kashmir are old orographic lake basins. In the former, no lake 
remains, as the barrier has been cut down and all the space between 
the enclosing ranges converted into great meadow-like plains ; in 
1 Kul (kal, gul, gueul), nor (noor), tso (cho) mean lake in the various languages of 
Central Asia. 
2 Foster and Whitney, Rept. on Geol. of Lake Superior, 1850, pt. ii, 117. Ramsay sees 
no necessity for excepting this lake from a glacial origin. Phys. Geol. and Geog. Gr. 
Britain, 1872, 176. 
3 A. Agassiz, Proc. Amer. Acad., xi, 1876, 283. 
