ARCH^AN GROUP. 269 



of West Texas, as reported by Messrs. Dumble and Streeruwitz, I think we 

 may justly conclude that we have here only the accumulations of the eastern 

 shore area of the Fernandan Period. New evidence is thus afforded of the 

 elevation of a continental mid-rib, such as Dr. Dana has suggested, at the 

 close of the Burnetan (Laurentian?) Period, and before the deposition of the 

 great system of Ontarian? strata which we are now considering. Incident- 

 ally, we also have a suggestion of a near continental land area during the 

 Fernandan Period in the nature of the extensive detrital shallow water beds 

 which compose a considerable part of the strata of that system. Whenever 

 the Fernandan Beds are visible in connection with the Burnetan strata, 

 through their own excessive erosion or by reason of the persistence of prior 

 elevations of the earlier system, there is always abundant evidence of uncon- 

 formity; and if any fractures occur, the joints of the northwest (Fernandan) 

 trend invariably cross and cut the strike of the Burnetan rocks. A very in- 

 structive illustration of the relative ages of the two Archaean trends may be 

 seen in an exposure of the Burnetan basal gneiss a little south of Lone Grove 

 Postoffice, Llano County. Here, upon the left bank of Little Llano Creek, 

 contortions in the gneiss are visible, deflecting the strike from north 75 de- 

 grees west to north 36 degrees west. Sometimes, as in the upper valley of 

 Little Llano Creek, there are appearances of faulting, but I have not yet de- 

 tected any well marked break of this kind which is certainly referable to a 

 Pre-Cambrian period. There is a well-nigh insuperable difficulty in determin- 

 ing such nice points of structure in rocks which partake so much of the same 

 texture as do the juxtaposed strata of these two systems. But occasionally a 

 belt of the later set cuts through the older trend in such a manner as to prove 

 at least a subsequent movement. By combining the two classes of evidence, 

 although no one observation may of itself settle both questions, we can be 

 certain that our postulates are strictly correct. Additional support is gained 

 from the fact that contortions occur in the lower system only where this or 

 later trends affect its continuity. Moreover, the composition and texture of 

 the Fernandan Beds is to a large extent that of derivatives of the Burnetan 

 lithologic series. 



Broad belts of the Fernandan strata cross the area indicated by vertical 

 hachures upon the progress map between the meridians 98 degrees 30 min- 

 utes and 99 degrees, and traces or isolated exposures are encountered farther 

 west. As indicated by the successive repetitions of characteristic strata in 

 uniform, direct and reversed order, and by the very steep dips in places, 

 there are several parallel folds. The great amount of denudation, the re- 

 stricted distribution of the succeeding rock system, the absence of Cambrian 

 and later strata, as well as the loci of the subsequent dynamic events, all seem 

 to imply that a large portion of the tract described has not been submerged 



