266 M. 1. Goldman — Catahoula Sandstone of Texas. 

 The results are given in the accompanying table. 





No. of grains 



Per cent 

 in each portion 



Equivalent 



percentage 



of whole rock 



Percentage of 

 different 

 feldspars x 



Portion 



Fresh 



Medium 



Weathered 



Fresh 



Weathered 



Fresh' 



Weathered 



Orth. 

 86 



79 

 87 

 93 



Micr. 



13 

 19 

 13 



2-5 



Plag. 



Medium 

 Fine 



Very fine 

 Extra fine 



63 



47 



48 



105 



29 

 50 



4-7 

 129 



60 



57 

 55 



70 



51 



47 

 48 

 56 



49 

 53 

 52 

 44 



5-3 

 25-1 

 16-3 



1-1 



5-1 

 28-3 



17-7 

 •9 



1 

 2 

 

 4-5 



Total 







47-8 



52-0 





1 Orthoclase means feldspar showing no twinning, microline means 

 " grating structure" twinning, plagioclase means polysynthetic twinning. 



Thus while obtained entirely without regard to each other 

 the results for the different portions show a fairly good corre- 

 spondence. The appearance of greater freshness in the " extra 

 fine " which seems to be supported by the higher percentage 

 of plagioclase in that portion may be due to errors of observa- 

 tion resulting from the smallness of the grains. Thus a small 

 fragment out of a cloudy feldspar might appear fresh and in a 

 small fragment of microcline the twinning in only one direc- 

 tion might appear. 



Ratio of different species of feldspar to each other. — At 

 best these figures for the proportion of the different kinds of 

 feldspars are to be regarded only as the merest approximations. 

 How much the number encountered is a matter of chance was 

 shown by two slides of the "extra fine" sand, in one of which 

 there were 9 plagioclases (only two of them regarded as doubt- 

 ful) among 68 feldspars counted, while in another were only 

 2 (both doubtful) among 182 feldspars. 



Heavy Minerals: Proportion of heavy minerals. — The 

 separation of the heavy minerals from quartz and feldspar in 

 the very fine sand gave the following percentages : 



Observed Corrected* 



Light 97*50$ 98'90 



Heavy 0*95$ 1-10 



Loss _. T55$* 



100-00 100-00 



* The loss is due to the large amount of handling in this separation and if 

 distributed pro rata gives the results in the second column. 



