June 4, 1897.] 



SCIENCE. 



885 



and in Maryland it includes portions of St. Mary, 

 Charles and Calvert counties. It lies entirely 

 within the Costal Plain area. The Potomac 

 river extends northwest and southeast across the 

 middle of the area; the Patuxent river crosses 

 its northeastern corner, and the Rappahannock 

 river crosses its southwestern corner. To the 

 extreme northeastward it extends to the shore 

 of Chesapeake Bay. These waters are all tidal 

 estuaries. Along the river valleys thereare wide, 

 low terraces, capped by the Columbia forma- 

 tion, of Pleistocene age. The intervening areas 

 are plateau remnants, capped by Lafayette de- 

 posits, of supposed Pliocene age. The under- 

 lying formations are the Chesapeake and Pa- 

 muukey, the latter extending from the west- 

 ward only a few miles into the area, along the 

 north side of the Potomac river. 



The Pamuukey formation, of which only the 

 uppermost beds are exposed, consists in greater 

 part of glauconitic marls of Eocene age. It is 

 overlain unconformably by the Chesapeake 

 formation, which is characterized by fine sands, 

 marls and clays, portions of which consist 

 largely of diatomaceous remains. The forma- 

 tion is very fossiliferous at some localities. Its 

 age is Miocene. The greatest thickness which 

 it presents in the Nomini area is about 270 feet, 

 but it continues to thicken gradually to the 

 eastward. 



The Lafayette formation, which ranges from 

 25 to 40 feet in thickness, consists of sandy 

 loams of orange, brown and buff tints, often va- 

 riegated, containing irregularly disposed bands 

 and sprinklings of small quartzite pebbles and 

 coarse sands. The pebbles and larger sand 

 grains are orange-tinted, mainly by superficial 

 staining. The plateau surface, capped by this 

 formation and deeply incised and dissected by 

 the larger drainage depressions, inclines gently 

 southeastward at an altitude ranging from about 

 190 feet along the northern and western border 

 of the area to about 90 feet along its eastern 

 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 val- 

 leys. 



The Columbia formation is a deposit of loam 

 merging downward into coarser materials con- 

 taining beds of quartzite, gravel and boulders. 



Its thickness averages about 20 feet. Its surface 

 extends from altitudes of 5 to 60 feet above tide 

 level. 



The principal economic features are under- 

 ground waters, which on the lower lands fur- 

 nish flows for artesian wells. Three water- 

 bearing horizons are known — one at the base of 

 the Pamuukey formation, another 100 feet 

 higher in the Pamuukey 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 supplies 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 to all of the 

 water-bearing horizons. 



Other economic resources of the area are 

 marls in the Pamuukey and Chesapeake forma- 

 tions, diatomaceous deposits in the Chesapeake 

 formation which are often sufficiently pure for 

 commercial use, brick clays, potters' clays, sand 

 and gravel. 



Folio 26, Pocahontas, Virginia-Wed Virginia, 



1S96. 



This folio, by Marius R. Campbell, consists of 

 five pages of text, a topographic sheet (scale 1 : 

 125,000), a sheet of areal geology, one of eco- 

 nomic geology, another of structure sections, 

 and, finally, a sheet giving a generalized co- 

 lumnar section of the district. 



The territory mapped and described in this 

 folio 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 uorthwest, and follows the irregular crests 

 of the ridges within the coal field. The south- 

 ern portion of this territory is within the limits 

 of the Appalachian valley, and its surface is 

 marked by linear mountains and narrow val- 

 leys, which are the characteristic forms of this 

 central division of the Appalachian province. 

 The northeru portion is within the Cumberland 

 plateau region, and its surface is that of a table- 

 land deeply dissected, so that it now presents 

 a confused mass of irregular ridges and hills, 



