Jgg CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Sierra Larga in the valley of the Salinas River near Her- 

 reras, and other similar hills along- the western margin of 

 the area as far south as the Conchos River. 



The Sierra de Pomeranes, east of Mendez on the Con- 

 chos, while composed principally of sediments of middle or 

 upper Eocene age and largely due to erosive action, seem 

 to be connected also with the Corcovado uplift and mark 

 the beginning of the influence of such orogenic movements. 

 These become more and more manifest toward the south 

 as shown in the Martines hills east of Abasolo and in the 

 San Jose de las Rusias hills, where igneous rocks make 

 their appearance breaking through the sediments of the 

 upper Oligocene. The northern half of the area is drained 

 by affluents of the Rio Grande. The most northerly streams 

 of interest are the arroyos de Caballero and del Amole, a 

 few miles south of Guerero. Following these the Salado 

 River, which drains the Sabinas and Esperanza coal fields, 

 crosses this belt and empties into the Rio Grande opposite 

 Zapata. The principal branch of this river on the south is 

 the Sabinas. South of these, the Salinas River (also called 

 the Pesqueria) coming in from the region just north of 

 Monterey, joins the San Juan near Aldamos. The San 

 Juan itself, which drains the area south of Monterey, flows 

 northeastward and reaches the Rio Grande at Carmargo. 

 South of the Rio Grande the only two important river sys- 

 tems are the Conchos and the Soto la Marina. The Conchos 

 heads west of Linares and, flov/ing north of the San Carlos 

 and Burgos groups of mountains, reaches the gulf by way 

 of Mendez and San Fernando, while the Soto la Marina, 

 rising just southward of Linares, flows southeastward by 

 way of Abasola and Soto la Marina, passes between the 

 Sierras de Martines and Tamaulipas and then turns east- 

 ward to the gulf. In its lowxr reaches the Conchos River 

 is sometimes called the Presas. Between these two rivers 

 is the arroyo Chorreras and south of them the Zarzizal, 

 which empties into Tordo Bay. 



