414 ABSTRACTS 



border. Its greatest altitude is 200 feet in a portion of Nomini 

 cliffs. It has also in most cases a slight slope into each of the river 

 valleys. 



The Columbia formation is a deposit of loam merging downward 

 into coarser materials containing beds of quartzite, gravel, and bowl- 

 ders. Its thickness averages 20 feet. Its surface extends from alti- 

 tudes of 5 to 60 feet above tide level. 



The principal economic features are underground waters, which on 

 the lower lands furnish flows for artesian wells. Three water-bearing 

 horizons are known, one at the base of the Pamunkey, another 100 feet 

 higher in the same formation, and a third in the lower sandy members 

 of the Chesapeake formation. They all dip to the eastward at a very 

 moderate rate. There are many artesian wells which obtain water sup- 

 plies from 160 to 305 feet. On the artesian well sheet of the folio 

 distinctive underground contours are given to show the depths below 

 tide level of all of the water-bearing horizons. 



Other economic resources of the area are marls in the Pamunkey 

 and Chesapeake formations, diatomaceous deposits in the Chesapeake 

 formation which are often sufficiently pure for commercial use, brick 

 clays, potter's clays, sand and gravel. 



Geologic Atlas of the U?iited States. Folio 26, Pocahontas, Virginia- 

 West Virginia, i8g6. 



This folio, by Marius R. Campbell, consists of five pages of text, 

 a topographic sheet (scale i : 125,000), a sheet of areal geology, one of 

 economic geology, another of structure sections, and, finally, a sheet 

 giving a generalized columnar section of the district. 



The territory mapped and described embraces an area of 950 square 

 miles, the southern portion of which is in Virginia and the northern 

 portion in West Virginia. It is located west of New (Kanawha) River 

 at the place where the state line leaves East River Mountain, the last 

 of the valley ridges toward the northwest, and follows the irregular 

 crests of the ridges within the coal field. The southern portion of this 

 territory is within the limits of the Appalachian valley, and its surface 

 is marked by linear mountains and narrow valleys, which are the 

 characteristic forms of this central division of the Appalachian prov- 

 ince. The northern portion is within the Cumberland plateau region, 

 and its surface is that of a tableland deeply dissected, so that it now 



