SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1021. 



In this log the thickness of roclvs represented 

 by the sample is hiid of! vertically to scale as 

 the vertical coordinate. The width of the 

 column represents 100 units, and the percent- 

 age of each of the three constituents in each 

 sample — the lime, clay, and sand — is laid off 

 horizontally across the middle of the space 

 representing the sample. - 



To obtain these results the samples were 

 examined with a hand lens, which was some- 

 times supplemented by a binocular micro- 

 scope. As many types of rock as could be 

 recognized W(M-e listed, and the proportion of 

 each was estimated. I^'ragments of peculiar 

 types and at intervals of the prevailing ty]K's 

 were selected to he made into thin sections, 

 which were examined under the compound 

 microscope, and tiie ])roportions t)f sand, clay, 

 and lime in them were estimated. As the 

 work progressed it was found desiral)le to in- 

 crease the immber of thin sections, even of 

 prevailing types from successive samples, as 

 changes in sandiness might otherwise not be 

 recognized. 



The samples examined were obtained from 

 the Seaman well No. 1. in Palo Pinto County, 

 and the Rudd well No. 1, in Comanche County. 

 As those from the Seaman well were the iirst 

 to be studied the observations on them are 

 somewhat less accurate than those on the 

 Rudd samples. 



This method of determining the proportions 

 of the three ingredients is obviously a rather 

 rough one, yet 1 think it is justified by the 

 results, for it brings out correlations with re- 

 markable detail. It has even certain advan- 

 tages over the mechanical and chemical analy- 

 sis employed in the method described by Trager 

 in the pa|)er just cited. Certain changes, es- 

 pecially silicilication, which tend to unite the 

 original constituents of the rock so that they 

 can not l)e separated or wliich replace them by 

 other substances, interfere, according to the 

 extent to which they are developed, with the 

 correct mechanical or chemical determination 

 of the composition of the rock as it was when 

 deposited, but these changes are not likely to 

 interfere nearly so much with the microscopic 

 recognition of the ingredients, especially of 

 clay and sand. In much chertilied beds any 



2 Tllis mpthiKl of reprcsfiitalion is described by E. A. Trager in A 

 laboratory method for Iheoxamination of well euttings: Econ. Geoloj^, 

 vol. 15, pp. 170-176, lllUO. 



nnitine mechanical or chemical analysis would 

 seem to be almost useless as a means of deter- 

 mining the original composition. On the other 

 hand, the determination of the proportions of 

 the ingredients In' the eye may be veiw inac- 

 curate, especially in an argillaceous rock, as 

 clay may form a dark stain and veil the pres- 

 ence of other constituents. In work on the 

 t)lack limestones that are so abundant in the 

 "Bend series" there is the added difficulty of 

 distinguishing between organic staining matter 

 and clay. The most accurate method of de- 

 termining the i>roi)ortions of the constituents 

 sought would undoubtedly be a combination 

 of observation in thin section with chemical 

 and mechanical analyses, but circumstances 

 did not ]iermit me to use the latter methods. 

 The method useil, however, probably does 

 bring out relative composition, which is the 

 essential fact in tliis investigation. 



Where distinct fragments of flint could be 

 recognized in the sample their proportion was 

 estimated and represented separately, merely 

 because they could not properly be classed 

 with the other tlu'ee constituents. It is my 

 belief that flint is produced by the silicifica- 

 tion of sediments after their deposition and 

 that for the purpose of the present investiga- 

 tion it should be regarded as replacing lime. 



The flint estimated represents only the pro- 

 portion of its individual particles, not the 

 degree of silicification of the sample. Incip- 

 ient chertification was recognized in many thin 

 sections made from samples in which no frag- 

 ments of flint could l)e found. In general this 

 microscopic chertification is greater in the 

 lower part of the geologic section, increasing 

 downward as the beds carrying distinct flint 

 are approached. It is therefore not surprising 

 that the highest occurrences of fragments of 

 flint should be at different horizons in the two 

 wells— at 2,738 to 2,745 feet in the Rudd well 

 !ind at 4,090 to 4,100 feet in the .Seaman well. 



Although the assumption that variations in 

 the proportions of the principal constituents of 

 these beds would be recorded in widely sepa- 

 rated parts of the basin in which they were 

 deposited proved, in a general way, to be 

 remarkably well justified, there is one respect 

 in which it requires restriction and interpreta- 

 tion. It might, indeed, have been expected 

 that lime, which is not a true sedimentary 

 constituent but is mostly of organic origin, 



