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



General character of products. — The coarse sand (4 grains 

 as noted above) consists of agglomerations of sand in a d'ull 

 olive-green matrix which did not effervesce in HC1 but gave a 

 yellow stain to the acid. 



All the other portions, of which the characters are now to 

 be described, consisted mainly of quartz and feldspar. 



b. Microscopic Examination. — Rounding of the grains: 

 General appearance. — The exquisitely perfect rounding and 

 smoothing of many of its grains is a striking feature of this 

 sandstone. 



Proportion of rounded grains present. — A count, in the 

 different portions, of the proportion of quartz grains that were 

 rounded, gave the following results :* 



2-8 per cent of total sand. 

 13-3 " " " " " 





Percentage of 

 rounded grains 

 in the portionf 



Medium 



27 



Fine 



25 



Yery fine 



Extra fine 



35 

 35 



11-9 



0-7 



U (( 



28*7 Per cent of rounded 

 grains in the total 

 sand. 



Lower limit of rounding. — The smallest rounded grains 

 found measured about 0-035 mm in diameter and were scarce, 

 but grains of O05 mm diameter were not uncommon. 



landaises No. 41 Buitenzorg, 1910), who devised them independently. 

 Entirely similar diagrams, however, differing only in scale, were used at an 

 earlier date by Udden. (See footnote pp. 267, 268. ) Their construction can be 

 most readily grasped by conceiving of the vertical columns as being actually 

 the portions of sediment they represent, set up side by side in cylindrical 

 tubes of the same diameter. The columns are all of the same width and 

 represent material ranging in size between the diameters indicated at each 

 side of them, while the vertical distances represent percentages to scale. 



* The quartz was readily differentiated from the feldspar by immersing 

 the grains on the slide in a liquid whose index of refraction was 1*548, the 

 mean index of quartz. 



f In these counts all grains that might be called subrounded were counted 

 with the round grains, while those that seemed more subangular were 

 classed as angular. Largely this classification depended on the appearance 

 of the upturned surface. As this could not be well studied under the high 

 power (No. 7 objective) used on the " extra fine" sand, the count of this 

 size is more uncertain. Perhaps that explains the high percentage of rounded 

 grains counted there, where a lower proportion than in the coarser sizes 

 would be expected. 



In the " fine " sand a count was also made of only those grains that showed 

 complete rounding and 12 per cent were found, i. e. just about half that 

 given above. This relation therefore affords a factor that may 'be used for 

 an approximate estimate of the proportion of completely rounded grains 

 present in the entire sand. In the "fine" sand also a count> of the ratio 

 of all rounded grains (feldspar as well as quartz) to all angular, gave exactly 

 the same proportion as for quartz only. 



