342 PROCEEDINGS OF THE ACADEMY OF [1893. 



represents a marine formation of Quaternary age, but without being 

 able to disprove this I would suggest another cause which seems 

 equally possible. It seems to me that this is no more than a gravel 

 slope formed in part from the wash from the mountains, but having 

 chiefly been brought down by the mountain streams and deposited 

 in their channels, which have since been abandoned. Just such 

 deposits are at present found in the broad stream valleys and if they 

 should abandon their course the present stream bed deposits would 

 remain to cap the hill tops when the general level of the region was 

 lowered. 



(d) Desslcated Quaternary Lakes. — There are in this region many 

 lake basins of Quaternary age. One of these, Crow Flat Valley, I 

 have studied in part. The fault scarp of the Guadalupe Mountains 

 and the foot of the hills at its base form the eastern boundary of 

 this lake. The other enclosing walls I have not seen. It is in part 

 a synclinal valley formed by the dragging up of its strata on the 

 east by the Guadalupe fault. The Crow Flat is a level plain, 

 deeply filled with silt, at least forty feet deep, of a very fine quality, 

 and having shore lines and deltas on either side. Its extent I am 

 unable to state even approximately. 



The lake is not quite extinct. It is a catchment basin for a large 

 area and water is found throughout the valley at a depth of from 

 five to forty feet in the lake silts. It is invariably alkaline, fre- 

 quently saline. In the lowest portion of the valley the water comes 

 to the surface in a great salt, marshy area, upon which a crust of 

 salt exists. Alkaline flats and marshy areas are common, and gyp- 

 sum deposits occur in several places. There is a gypsum stratum 

 quite uniform in extent and in one place a dune-like accumulation 

 of gypsum sand. This is but one of a series of dessicated lake 

 basins in this region, none of which have been studied except in a 

 hurried reconnoissance. 



(e) The Bio Grande and Bio Pecos. — I am unable to say any- 

 thing about the Rio Grande and Pecos Rivers in Texas. Both of 

 these rise in the northern regions, in the mountains, and enter 

 Texas as well defined and overburdened streams. Their Texas 

 tributaries are nearly all of the arid arroyo type, carrying water 

 only in times of heavy rains. Of these two large rivers I have seen 

 only enough to convince me that they have an interesting history, 

 but my knowledge of them is too indefinite to admit of the statement 

 of my suspicions concerning this history. 



