286 CENTRAL MINERAL REGION OF TEXAS. 



its outcrops. But the compact character is not a local feature like a certain 

 other effect often observed where this stratum is in actual contact with pro- 

 trusive granite. On the top of Sandy Mountain, and particularly on and 

 about a little knob to the north of it, this Hickory layer has been consider- 

 ably altered by heat so as to exhibit in different parts a gradual transition 

 from above downwards, between the compact massive sandrock and a rock 

 which most lithologists would class as a granite. Similar conditions exist on 

 Sharp Mountain, House Mountain, Smoothing Iron Mountain, and elsewhere, 

 but not on Packsaddle Mountain. 



These facts taken together, in view of all the known occurrences of the 

 Hickory strata, give the only lucid explanation of the situation, and one 

 which has required more detailed study than almost any other problem con- 

 nected with this district, and it has been puzzling to decide whether the two 

 or more lines of protusion of granite of undoubted Post-Hickory age are the 

 cause of the unconformity succeeding that epoch, or if they may not oe of 

 very much later date.* 



But now it seems clear that the pulsations of the granite magma produced 

 several broad folds in the Hickory strata, leaving certainly two great syncli- 

 nal basins to be afterwards partly filled by the later Cambrian sediments. 

 One fact, although not of itself a perfect proof of this postulate, affords ex- 

 cellent confirmatory evidence. This is the absence, in every case, of any later 

 than Hickory sediments from the granite ridges now capped by them, ex- 

 cepting, of course, in the rare instances where uplifts in the later trends may 

 have raised them to view. The thickness of the Hickory Beds, all told, can 

 not well be above 200 to 250 feet. I should put it nearer 150 feet, judging 

 from the best exposures, but in places where it is most altered by heat it is 

 usually difficult to determine its basal members. On Packsaddle Mountain 

 there is less than 100 feet of it between the Texan strata beneath and the 

 higher Cambrian above, but the basal conglomerate is absent in these sections, 

 as well as some coarse white false-bedded sandstone elsewhere observed. The 

 Hickory Creek section is the only complete one yet observed, but some of 

 the strata there exposed are more developed in other localities. 



No fossils have been taken from any of the Hickory Beds. 



(2) THE KILEY SERIES (MIDDLE CAMBRIAN?). 



On Packsaddle Mountain, at the east end of the eastward projection, the 



*This difficulty is enhanced by the apparent fault lines following the same north-south 

 course, which, if they be true faults, must have originated as late as the Silurian period. For a 

 long time the writer was unable to explain this feature satisfactorily, but now that the early 

 Cambrian uplift is understood, other troublesome points concerning the later structure are 

 made to disappear. 



