darton.] CONDITIONS AFFECTING WATERS. 19 
Richmond, Weldon, and Columbia to Augusta, Ga., aud thence through 
central Georgia and Alabama, and they extend westward up the gentle 
slope of the Piedmont plateau to the base of the Ax^palachians. To 
the east the crystalline floor sinks to a great depth, and it is about 
2,000 feet below the surface along the ocean shore south from New 
Jersey. In fig. 1 a typical cross section of the Coastal Plain province 
is given. 
The sedimentary deposits are a succession of widely extended sheets 
which usually thicken to the east and dip gradually to the east and 
southeast. In their usual relations they comprise alternating beds 
of coarse and fine deposits, of which the coarse materials are water- 
bearing and the fine materials, on account of their relatively impervious 
nature, serve to confine the waters in the coarse beds. The eastward 
inclination of the beds determines the direction of flow, and as the 
watersheds or surface outcrops are in the higher lands to the west, the 
waters often have sufficient pressure to rise above the surface from 
wells in the lower lands. 
On the floor of crystalline rocks there appears to be an almost gen- 
eral occurrence of coarse water-bearing beds which are overlain by 
clays and fine sands. At various intervals above there are other coarse 
beds of greater or less extent containing water supplies for deep wells. 
The order and thickness of the beds vary in the different portions of 
the region, and present local features which will be described in the 
several chapters that follow this general introduction. 
SOME CONDITIONS AFFECTING SUBTERRANEAN WATERS 
IN THE COASTAE PEAIN. 
Before proceeding to the well records and to a consideration of their 
significance it may be well to point out some conditions which affect the 
occurrence of subterranean waters. I shall notice only a few points 
here, and those who are interested in a more extended discussion 
should read the paper by Prof. T. C. Chamberlin, entitled u The requi- 
site and qualifying conditions of artesian wells." 1 
The simplest condition of underground waters is shown in section 1 
of fig. 2. The water enters the coarse stratum at its outcrop over the 
belt, A A, and flows down the dip, being confined to the coarse stratum 
by impervious materials above and below. When it is tapped at B it 
rises to a level approximately as high as AA. On the Coastal Plain 
there are probably several qualifying conditions of greater or less 
importance. The first is shown in section 2 of the figure. This repre- 
sents a diminution in the coarseness of the materials down the slope, 
until finally the bed becomes so fine-grained as to be impervious to the 
water. Under this condition a well at C would afford water, but one 
Fifth Ann. Rept. U. S. Geol. Survey, pp. 125-174, 1885. 
