December i, 1893.] 



SCIENCE 



297 



SCIENCE: 



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TEXAS GLAYS AND THEIR ORIGIN. 



BY W. KENNEDY, AUSTIN, TEXAS. 



A SHORT time ago, while engaged in making a report on 

 the clays of the State for the Geological Survey of Texas, 



1 had occasion to study a large number of analyses made 

 of clays belonging to the different Tertiary formations. 

 During the course of the investigations it appeared to me 

 that there w&s a peculiarity in the chemical composition 

 of these clays not often seen among clays — that is, while 

 in nearly every other clay to the analysis of which I had 

 occasion to refer, and in which the alkalies, potash and 

 soda were separated, the contained potash appears to ex- 

 ceed the percentage of soda, and in some instances this 

 excess apj)ears to be very great. In the Texas Tertiary 

 clays, on the other hand, almost every one of the analyses 

 made shows the soda to exceed the potash in ratios from 



2 to 5 of soda to 1 of potash. As this excess varies in the 

 different divisions, the difference generally increasing as 

 we ascend in the beds, while at the same time the actual 

 quantities of both decrease in the same ratio until the 

 highest or coastal clays are reached, when the amounts of 

 both are largely increased, I have been led to the opinion 

 that this peculiarity might be due to the origin of the 

 materials forming these deposits, or that some clue to 

 their source might be obtained by a study of this 

 phenomenon. 



With this object in view, I have examined whatever 

 analyses have been available of the deposits underlying 

 or older than the Tertiary within the State, as well as the 

 analyses belonging to the Tertiary and other beds found 

 in the other States, so far as I have been able to obtain 

 them, together with the analysis of the underlying de- 

 posits from which the clays may reasonably be expected 

 to have been derived. 



In the New Jersey clays, which, according to Cook, are 

 of Cretaceous age and derived mostly from rocks lying to 

 the southeast of the deposits, but which are now covered 

 with water, or else completely destroyed, the jjercentages 

 of potash and soda are 0.93 potash and 0.10 soda. In 

 Ohio, according to Mr. Orton, the clays derived from 

 the Carboniferous shales show averages of : 



5- Fire clays, - 

 8. Potters' clays, 

 6. Pipe clays, - 



Or an average of 



In Kentucky, the next report examined. Dr. Peters 

 shows the averages of the different formations to be: 



10. Tertiary fire clays, 



17. Coal-measure fire clays, - 



5. Tertiary Potters' clays, - 



3. Coal-measure Potters' clays, 



3. Black slate and Clinton clays, 



I. Middle Hudson clays, 



In Arkansas, according to Williams, the 

 percentages of potash and soda to be: 



At Little Rock, 



Round Mountain, 



Fort Smith, - - . - 



These shales belong to the Carboniferous, and it may 

 be noted that the shales in the neighborhood of Little 

 Rock are in close contiguity to the syenite area around 

 Eourche Cove. Unfortunately no clay analyses showing the 

 exact relations between the potash and soda in the Ter- 

 tiary deposits are available from either Arkansas or 

 Louisiana, into which many of the Texas Tertiary beds 

 stretch with unbroken continuity. 



Coming back to the fact that the Texas Tertiary clays 

 are sodic clays, it is interesting to note that the immedi- 

 ately underlying deposits of Cretaceous age also carry an 

 excess of potash over soda. The section of these beds 

 appears to be roughly, in descending order, thus: 



Greensand marls. 



Marly flags, 



Ponderosa (blue) marls, 



Chalk marls, 



Austin limestone. 

 The published analyses of these deposits show the per- 

 centages of potash and soda to decrease as we descend as 

 follows: 



Greensand marls, - - - 



Ponderosa (blue) marls, 



Chalk marl, . . - - 



Austin limestone, . - - 



Average Cretaceous, - - - 0.733 2.72 



Going still further back in the deposits, the only 

 analyses we have of the clays and shales of the Carbon- 

 iferous show them to be also sodic and to carry a percent- 

 age of 3.09 soda and 1.53 potash, or closely approximating 

 the ratio shown in the Tertiary basal clays and the lignitic 

 beds. 



The only analyses we have of the Texas kaolins show 

 the west Texas materials to be practically free from 

 alkalies and the Edwards County deposits to carry 0.02 of 

 potash and 0.60 soda. An analysis of the base It from 

 Pilot Knob, near Austin, gave Professor Kemp 2.77 soda 

 and 2.02 potash {Amer. GeoL, Nov., 1890). A kaolin from 

 Pulaski County, Arkansas, shows 0.23 potash to 0.37 soda. 



Clays naturally partake of the nature of the rocks from 

 which they may have been derived, and the proportions of 

 their constituents will in the same manner be in a ratio 

 more or less in accordance with those of the parent rock, 

 the variations being due to the solubility of the constitu- 

 ent and the number of changes to which it may have been 

 subjected during the course of its transportation from the 

 original locality to that in which we may find it. These 

 changes are, however, sometimes extremely great, as, for 

 instance, in the case of kaolin. Williams shows a kaolin 

 in Arkansas, evidently derived from a syenite containing 

 5.48 potash and 5.96 soda, to have only 0.23 potash and 

 0.37 soda. 



Since, then, the Texas Tertiary clays appear to be sodic. 



