262 M. I. Goldman — Catahoula Sandstone of Texas. 



I. Description. 

 1. Undisint eg rated Rock. 



Macroscopic examination. — The sandstone is light colored, 

 yellowish, with faint lavender tinges and pale brownish 

 patches irregularly distributed through it. 



As a quartz sandstone it appears rather pure, though 

 speckled with opaque white and with fairly abundant black 

 grains. It is often very friable on an edge but not in larger 

 fragments. Absence of bedding, or better perhaps of lamina- 

 tion, is evidently characteristic for the rock, as fragments 

 of 4 inches or more in diameter show no trace of it in any 

 direction. This is especially evident in the pieces containing 

 impressions of fossil nuts. Here too, the lack of orientation 

 is brought out by the nuts themselves, which lie with their 

 long axes showing only the slightest evidence of parallelism. 

 In some specimens impressions of fossil leaves show even 

 more random arrangement as they are not only not parallel to 

 each other, but even the surfaces of the individual leaf imprints 

 are strongly curved or curled. Certain specimens, however, 

 differ in these respects from the majority, for in them the leaf 

 impressions are rather numerous and closely packed approxi- 

 mately parallel to each other. They are not, however, distrib- 

 uted on any bedding planes marked by difference of texture in the 

 sand itself. Moreover, even where most pronounced this paral- 

 lelism is not absolute, and the surfaces of the leaves are not 

 perfectly flat. 



Often associated with bunches of parallel leaves are rather 

 abundant small grains or pellets (up to about 8 mm diameter) of 

 a soft, crumbly, yellowish-white, argillaceous material. 



Hand-lens exa?nination. — The lavender tint is seen to be due 

 to the cement, apparently of opal, binding the grains. Its dis- 

 tribution is very irregular, and where it is lacking the rock is 

 friable. In places the cement is more opaque, whitish, resem- 

 bling in appearance the clay pellets described above ; where 

 these are abundant the cement also takes this character. But 

 the two types of cement, the opaline and argillaceous, grade im- 

 perceptibly into each other, and it is quite possible that the opa- 

 line variety is derived from the argillaceous. 



2. Disintegrated rock. 



a. Mechanical analysis. — Whether opaline or argillaceous the 

 cement should decompose on being boiled with a strong solution 

 of KOH and trial showed that it does. A mechanical analysis 



