GEOLOGY OF GILES COUNTY, VIRGINIA 
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type of drainage, many great springs are found bordering the 
New River, and small tributaries are uncommon in the limestone 
areas. The New, itself, seems to vary greatly in size over 
small areas. The writers believe that this is due to the fact that, 
some of its water, at places, flows underground or in crevices for 
a distance, only to join the surface waters of New River again 
in the form of great springs, some of which may be hidden but 
many of which are visible. Of course solution topography and 
underground waterways could not be developed much below the 
water table. 
No typical karst topography has developed in Giles County, 
but the sink hole areas are usuafly turned into grazing lands 
since the soil mantle is too thin to be easily cultivated. 
STRATIGRAPHIC GEOLOGY 
INTRODUCTION 
In Professor W. B. Rogers’ classification of the geological 
formations appearing west of the Blue Ridge in Virginia, four- 
teen groups of strata were given numbers, beginning with the 
oldest. His brother. Professor H. D. Rogers, divided the Paleo- 
zoic rocks of Pennsylvania into fifteen sets, “extending from the 
deposits which witnessed the very dawn of life upon the globe, 
to those which saw the close of the long American Paleozoic 
day.” Thus the names of these formations were the various 
parts of the day, instead of the ordinary geographic terms used. 
Extremes, then, of his classification were Primal, signifying the 
dawn (that is, tower Cambrian), and Serai, meaning night (and 
corresponding to the coal-measures.) In the literature of Vir- 
ginia, both systems have been used. A table is introduced here 
to show the relation between these classifications and the one 
now in use. 
The rocks of Giles County comprise all of the divisions of the 
Paleozoic from lower Cambrian to the lower Carboniferous in- 
clusive, No younger consolidated strata are found, but some 
Tertiary gravels are present, which may be the approximate 
equivalent of the so called “Orange Sand” found in the. states 
further west. Limestones are quantitatively in predominance 
in Giles County, being especially well developed in the older Pal- 
eozoic divisions. Besides limestones, there are shales, cherts, 
