ARCHEAN GROUP. 557 



hereafter prove inapplicable, and also because it is as yet impossible to make 

 wholly satisfactory comparisons with the strata of remote areas, local names 

 have been chosen to designate systems, series, and divisions. In a general 

 way these terms also serve to indicate the strata which are abundant in par- 

 ticular localities; but it must not be inferred that these titles are ordinarily 

 comprehensive enough to include the whole range of any terrane, although it 

 may be so in individual cases. Thus the Fernandian system is named from 

 excellent exposures of the rocks in a portion of the drainage area of San Fer- 

 nando Creek, in Llano county, but this region by no means monopolizes the 

 outcrops of that system, nor do the names Lone Grove, Iron Mountain, Llano, 

 Katemcy, etc., respectively indicate the only localities in which the rocks des- 

 ignated by these cognomens are visible. The same remarks apply with equal 

 force to all the nomenclature adopted for the various rock stages in our region. 

 The Taxonomic Chart* gives a condensed view of the geologic divisions as 

 they have been worked out by the writer, corrected to January 1, 1891. 

 This varies but little from the arrangement given in the First Annual Re- 

 port, Plate III, but it may perhaps be found more convenient for reference, 

 and its introduction into this volume will also facilitate the use of the geo- 

 logic map of our region, j- 



*The original names Burnetan, Fernandan, Texan, Niagaran have been changed to termi- 

 nate in ian, to conform to the requirements of the International terminology. 



f At the last moment it was found necessary to omit the coloring of the topographic map 

 (Plate XXIII) which was prepared to illustrate the geology of this district. 



