ARCHAEAN GROUP. 



263 



nized, by indications of the pseudo-igneous character of the Lone Grove and 

 Bodeville strata, but our knowledge is too meagre to make this possibility a 

 basis for taxonomic adjustment. It may very well be that the gneisses and 

 their superincumbent beds have been altered from a sedimentary condition, 

 although they seem to agree well with Mr. Lawson's section, which he does not 

 so interpret. But he does not speak of such stratigraphic evidence as we 

 have in our area of the continuity of the schists across the folds. 



Plications and contortions of comprehensive extent are not characteristic 

 of these strata in Central Texas, although they occur locally where the]?- 

 origin is readily explained by subsequent dynamic events. 



From what has been presented, the writer feels warranted in making the 

 following conclusions, namely: (1) That over a limited area of Burnet 

 County, a large portion of Llano County, and much of Mason County, there 

 is a system of rocks composed of three fairly defined series, apparently con- 

 formable each to each, but lying unconformably below the succeeding strata; 

 (2) that these have once been continuous across the area of their present ex- 

 posures in Central Texas; (3) that they have been enormously denuded, 

 especially in the schistose portion; and (4) that they have been folded as one 

 subsequent to the deposition of the whole system. 



As a provisional arrangement the following taxonomy is adopted, with the 

 proviso that the author can feel almost as well satisfied, on some accounts, 

 with a scheme which restricts the term Laurentian to the Lone Grove strata, 

 and places the Long Mountain and Bodeville rocks in a separate system: 



Group (Era). 1 System (Period). 



Series (Epoch). 



Beds. 



ARCHAEAN. < 



BURNETAN, 



or 

 Laurentian? 



3. Bodeville. 



2. Long Mountain. 



1. Lone Grove. 



Mica and Chloritic Schists 



(chiefly Acidic). 

 Hornblende and Pyroxene Rocks 



(Basic). 

 G-neiss, Granite, etc. 



AGE OF THE IGNEOUS IRRUPTIONS.* 



In the Central Mineral region intrusive igneous rocks have played an im- 

 portant part in complicating the structure and in determining the subsequent 

 erosion. Aside from Buckley's announcement that most of the granites are 



* In this report a series of terms is used in reference to the igneous rocks, as indicated 

 below: 



An Irruption is understood to imply simply an igneous outburst, and an Irruptive its pro- 

 duct, without regard to the mode of action. 



An Eruption is here understood to mean a volcanic or fissure ejection, and its product is 

 termed an Eruptive. 



An Intrusion is, for our purpose, the forcing of an igneous mass into or between the 

 strata, and an Intrusive is the resulting mass. 



