PALEOZOIC GROUP. 301 



of the Burnet marbles, and it may be that this should be taken as the Cana- 

 dian-Trenton contact in Central Texas. Our studies have not yet gone far 

 enough to settle this question. In the upper part of the Hoover Division, in 

 McCulloch and San Saba counties and elsewhere, the marbles are evenly or 

 unevenly colored shades of blue, red, brown, and yellow, producing in some 

 cases a beautiful variegation in the same stratum, at other times uniform 

 tints, exhibiting alternations of color in sets of strata. 



(2) THE SAN SABA SERIES ( TRENTON?). 



Upon the southern border of the Central Texas Paleozoic region the Creta- 

 ceous strata lie for the most part directly upon one or other of the terranes 

 below the summit of the Leon series. Before the former were deposited 

 erosion had left a foundation of irregular outcrops of the various beds from 

 Archaean to Silurian at least, and the Mesozoic subsidence involved enough 

 of the Central area to allow the early Cretaceous sea to bathe the outskirts 

 up to the inner rim of Silurian and earlier rocks. Upon the northern bor- 

 der of our portion of the Central region the Cretaceous overlies the Carbon- 

 iferous, and a broad area of the higher Silurian strata is now uncovered in 

 that region. In the west and south, therefore, there are few exposures of 

 Paleozoic rocks higher than the base of the Hoover Division, but in the east 

 and north the whole Silurian System is well developed. The most complete 

 section will be obtained along a northwestern course from near the mouth of 

 Beaver Creek, in Burnet County, across the county of San Saba, passing 

 west of Latham Creek by way of Deep Creek to the San Saba River and 

 beyond. From the excellent field for the study of the higher beds, covering 

 a vast area in San Saba County and in much of the San Saba River valley, 

 including territory in the neighborhood of San Saba City, no more appro- 

 priate name can be given to the Series. We need more knowledge of what 

 lies out beyond the southern edge of the district surveyed in 1889, but it is 

 a very significant fact that only one or two exposures (upthrow faults) of the 

 San Saba Series west of the Colorado River have been reported, south of the 

 divide between the San Saba and Llano rivers. A straight line drawn from 

 the southeast corner of Concho County to a point in Burnet County four 

 miles south of Burnet will lie south of all the exposures. Upon the southern 

 border the elevation of the same stratigraphic horizon is full 300 feet greater. 

 These features of the present topography are the results, in large measure, 

 of events of Post- Silurian date, and yet they have a very important bearing 

 on the study of Silurian geology, for it is evident that even the latest faults 

 in a region like this would be guidea into courses materially dependent upon 

 previous history. The beds of the San Saba series consist of dolomites and 

 chert. No stratigraphic breaks indicating dynamic unconformity have been 



