EPARCH^EAN GROUP. 279 



existing in our area any one section from which the continuous record can 

 be made out. 



4. The conclusions here announced may require modifications after more 

 thorough examinations, guided by the knowledge already acquired, but it is 

 very probable that such changes as may be necessary will be rather serial 

 than systemic in their scope. For, with all the complications induced by 

 subsequent orographic movements, and notwithstanding the gradual approach 

 of Cambrian conditions in the upper beds, the stratigraphic relations are 

 plainly with the preceding group as now defined by geologists.* 



Mr. Walcott in his illustrated section of Packsaddle Mountainf has failed 

 to fully interpret the structure, because he saw only a part of one side, near 

 where the intermingling of strikes and the occurrence of blind faults have 

 much obscured the original Post-Texan uplift. Evidently all of his so-called 

 Llano strata are what are here classed as Texan, and the base of his Pots- 

 dam includes a considerable portion of our earlier Cambrian systems, as will 

 be explained elsewhere. (See Hickory Series beyond). He certainly did not 

 detect the south dip of 14 degrees in the Cambrian sandstones at the north- 

 west point of the mountains, where they are underlaid by the Texan Beds 

 dipping in the same direction from 24 degrees to 40 degrees; nor did he ob- 

 serve that the eastward dip of the Cambrian across a fault, but in the line of 

 his section, is underlaid by a steeper dip of the same nature in lower Cam- 

 brian and Texan beds. Owing to these facts, which yield the strongest con- 

 firmation of the views here expressed, a single Packsaddle section is not 

 enough to elucidate the structure. The Texan System can only be properly 

 correlated by patching together such scraps of evidence as are scattered over 

 our tract in these complicated upthrows. A very carefully prepared instru- 

 mental section is given in Figures 7 and 8, Plate II. This is the result of 

 the field work of five men for two days in this limited area, besides the most 

 accurate work of the same party for some time in the surrounding country. 



The rocks of the Texan System are chiefly siliceous, but shales and lime- 

 stones are not wanting. The data for a satisfactory lithologic classification 

 are not yet collected, and it is impossible at present to adopt serial or epochal 

 divisions of any permanent value. Roughly speaking, it may be said that 

 there seems to be a fairly defined set of micaceous sandstones, almost equiva- 

 lent to schists, but structurally more allied to sandstone. As a part of this, 



* Were it not for my own firm conviction of the greater importance of "cycles of deposi- 

 tion" and "migrations of species" than merely local stratigraphy as elements of classifica- 

 tion, there would he no need of any doubt upon these points. Maj. Powell's observations in 

 Arizona and New Mexico, as well as Walcott's, all favor the idea that our Texan Beds are 

 representatives of the shallow sea border of a great Algonkian ocean off to the west. 



fAmerican Journal of Science, vol. XXVII, 1884, p. 432. 



