68 A GEOLOGICAL SCBVET OF LAXDS 



3. Claj and marl with occasional grains of glauconite and with 

 bands of limestone, containing Ostrea diluviana, Esogyra 



ponderosa and other fossils 22 



2. Shaly chalk with some ledges of chalky limestone 38 



1. Hard chalky limestone with thin seams of marly clay 20 



Thickness of the Austin Chalk. 



This formation measures not far from 750 feet along the Rio 

 Grande. North of the Anacacho it is somewhat less than this. 

 But as the division between the Eagle Ford beds and the Austin 

 chalk is not well marked the combined measurement of these 

 two formations maj- be more accurateir given, and this is about 

 1050 feet. In the country north of the Anacacho mountains they 

 measure about 950 feet. 



THE UPSON CLAY. 



The Upson clay is a deposit which takes its name from the old 

 Upson postofHce in Maverick county.* It is the equivalent of the 

 Taylor marls of the central part of the state. Where weathered 

 and leached, as it usually is, it has a yellow color. TThen freshly 

 exposed, it is dark gray or greenish gray. In many place its 

 carries small flakes and crystals of gypsum and thin horizontal 

 seams of this mineral. Crystals of barite were also found. Its 

 characteristic fossils in this region are Exogyra pouderosa and 

 Ostrea larva, the latter having been noted only in the upper part 

 of the deposit, where it occurs in some sandy layers which were 

 seen on Elm creek and on Imperialist creek, from two to four 

 miles north of Paloma. 



Distribution. 



The country underlaid by this clay is quite extensive. It 

 comprises all of those flat lands which extend southwest, south, 

 and southeast from Spofford. This includes most of the land 

 drained by Canyon Grande, Hackberry creek. Cow creek, and 

 Imperialist creek, west of the Eagle Pass branch of the Southern 

 Pacific railroad. East of this road it includes all of the Snow 

 Tank pasture, and the north half of the Jarita pasture and the 

 west part of the Gilbeau pasture. East of Spofford it is seen in 

 Lindsay creek as far north as to survey 18 in block 8 and in Elm 

 creek to within a mile of the Southern Pacific railroad. From 



* This name was first used by E. T. Dumble, Director of the Texas GeoL Survey. 



