1893.] NATURAL SCIENCES OF PHILADELPHIA. 343 



S. — Absence of Large Lakes in Texas. 



It is a striking fact, that in a State covering an area as great as that 

 of Texas, there is not a single large lake. Almost every other geo- 

 graphic form is represented, often in great variety, and the climatic 

 conditions vary from moist to arid. 



The lagoons of the sea shore near river mouths and in other 

 favorable situations are perhaps the nearest approach to lakes in the 

 state. The youug land, as yet hardly land, encloses temporary 

 lakes of saline water, which on the one hand are liable to destruc- 

 tion by the sea, or on the other to be quickly filled by the sediment 

 of the streams. 



The Tertiary and Cretaceous plains have been raised above the 

 sea without sufficient structural features for lake formation. They 

 consist of gently dipping strata and the lakes, which may have 

 originally existed in early shallow inequalities, have been long since 

 removed by the establishment of drainage. In the flood plains of 

 the Tertiary district there are lakes of small size, according to Pen- 

 rose who writes 31 "lakes are of a very rare occurrence, and are 

 never seen except in river bottoms, where they form muddy lagoons 

 abounding in fish and generally fed by springs. They are often of 

 considerable depth, and are connected with the main river by nar- 

 row channels." It seems probable that these lagoons are unfilled 

 portions of abaudoned river channels. Penrose states that in the 

 Tertiary district he saw but one lake in the uplands, this amounting 

 to little more than a large spring, having a diameter of about two 

 hundred yards. 



In central Texas the river erosion has uncovered the Carbonife- 

 rous from beneath the Cretaceous, and the drainage, although super- 

 imposed, is establishing itself without the presence of lakes. In this 

 section, in places where side streams have been held back by the 

 effort of the main stream to overcome some barrier below, extensive 

 flood plains have been built up in the lower part of the valley of 

 the small stream and here lagoons and oxbow lakes are sometimes 

 found. This is the case in the lower Pecan Bayou and San Saba 

 River, both tributaries to the Colorado. These streams are laked in 

 their lower course by the upbuilding of the flood plain of the Colo- 

 rado due to the retardation in its down-cutting caused by the 

 Silurian barrier. During the dry season all the medium sized 

 streams of the semi-arid belt become a chain of lakes of extremely 



"First Ann. Report, Texas Geol. Survey, 1SS9, p. 1 1. 



