310 CENTRAL MINERAL REGION OF TEXAS. 



in this region were of a different character. Until special study has been 

 given to this matter the writer prefers to hold the view taken in this report, 

 chiefly because his notes as yet yield no certain evidence of such relations 

 between the undoubted and the doubtful Silurian as would seem to be required 

 by a different supposition. At the same time the fossils, and above all the 

 structural relations, lend much color to the hypothesis that the San Saba 

 series, or a part of it, is the representative of Post- Silurian (Niagaran) depo- 

 sition. More facts bearing upon this point will be collected for the next 

 report. 



1. DEVONIAN SYSTEM. 



At several points along the northern border of our district the contacts of 

 the Silurian (San Saba series) with overlying beds are different to what has 

 been reported elsewhere, and not what I have observed in other places. Be- 

 tween what Mr. Cummins and Mr. Tarr, as I understand them, assume for 

 the Siluro-Carboniferous contact in the region about the southwest corner of 

 Lampasas County, there is in some sections an important series of strata of 

 but little thickness, but containing fossils closely allied to Devonian types. 

 Neither of these gentlemen has examined the outcrops referred to, but Mr. 

 Cummins states, after seeing my collections, that a very similar rock under- 

 lies his so-called Carboniferous near Lampasas; this he included in his 

 Carboniferous section. The writer, being charged with the study of 

 the pre-Carboniferous rocks, has made incursions to the territory of 

 the later sediments only for the purpose of gaining assurance that no gaps 

 remained unfilled, and the possible occurrence of Devonian was not as fully 

 apparent in the field as it has since become by study of the specimens. 

 Special attention will be given to the subject the coming season, but it is pos- 

 sible now to announce the probable verification of Shumard's doubtful dis- 

 covery in San Saba County, and the extension of the outcrops into Mason 

 and Menard counties, and probably into Burnet and Blanco? counties. As 

 stated by Shumard,* the thickness of this terrane, if it be Devonian, probably 

 does not exceed fifty feet, although this estimate can not be regarded as 

 strictly accurate in the case of a system but little explored. 



All that has really been done to date is the discovery of a few localities in 

 which outcrops appear of unusual strata whose position is intermediate as 

 regards the San Saba series below and the known Carboniferous rocks above. 

 But there are grave difficulties in correlating observations which were scatter- 

 ing, confused as they also are by faults and varying contacts, as well as by 

 areal changes in lithologic complexion. Stratigraphically these rocks all be- 

 long with the Post- Silurian representatives, for they are unbroken by the 



* Transactions Academy of Science, St. Louis, vol. I, 1860, p. 613. 



