PALEOZOIC GROUP. 283 



III. PALEOZOIC GROUP. 



In view of the facts and conclusions yet to be given, it is important to call 

 the reader's attention to the prior denudation of the land surface, and to 

 the other conditions necessarily existing in order to sustain such life as was 

 characteristic of early Paleozoic Time. The environment most consistent with 

 known facts is about as follows: 



(1) A subsidence below sea level of parts of our district, but not the whole; 

 (2) an ocean temperature not essentially low, but cooled sufficiently to permit 

 the growth of fucoids; (3) a near land area exposing just such Pre-Paleozoic 

 Beds as are now uncovered in portions of Burnet and Llano counties; (4) 

 lines of weakness or of tendency to crack and slide, causing liability to fault, 

 along the three trends of the great Pre-Paleozoic uplifts; and (5) as a corol- 

 lary of the preceding, a certain likelihood of subsequent irruptions approxi- 

 mately in the latest course. 



The first three of these conditions will be amply verified by the facts ad- 

 duced concerning the earliest Paleozoic strata, but the last two postulates 

 may require a little notice here to elucidate some structural features now but 

 little understood. Just prior to the Paleozoic depositions the latest or north- 

 south trend was the "line of least resistance," and the one along which the 

 greatest effect would naturally be given to the "pulsations" of the igneous 

 magma. The long era represented by the widespread denudation of the 

 Texan strata, and the later subsidence of the region shows that there might 

 have been a tendency to outbreak along this latest Pre-Paleozoic trend. The 

 facts are much confused, and probably more observations will be necessary 

 to settle the interesting questions arising from the study of notes and collec- 

 tions. 



The folding at the close of the Texan Period took place along two or more 

 parallel lines, but the subsequent erosion must have left them with a slope 

 towards the west, unless some important westward land elevation ensued. Of 

 this there is convincing proof, although it is not easy to account for it except 

 upon the hypothesis of Post-Texan igneous action. Some evidence of such a 

 movement prior to the deposition of the Cambrian strata has been obtained 

 from an examination of the country westward, but the structure is obscured 

 by the resulting faults, and it is only proper now to say that granitic out- 

 bursts existed which might possibly have had much to do with the walling 

 in of the sea in the earliest Cambrian Epoch. 



3. THE CAMBRIAN SYSTEM. 



There was probably a westward elevation of the land after the era of 

 Eparchaean deposition, and the earliest Paleozoic Beds were laid down in a 



