ORDER OP THE PAMUNKEY BEDS. 483 



finding of marl, by boring in places where the existence was not 

 before known, and the variety or quality of whatever could be 

 so reached, were matters of chance. Of course all searches for 

 marl, by boring, were directed by no rule except that of selecting 

 surfaces of low level. And this one object was mistaken, and would 

 often cause the concealed marl bed to be missed by borings made in 

 its close neighbourhood. For if in land of alluvial formation, the 

 ancient flood most generally had swept off all the previously exist- 

 ing marl, and the vacancy so made was afterwards filled by either 

 the succeeding drifted earth, in part, or entirely by still later allu- 

 vial deposits. 



But if proper attention is given to the general dip of the whole 

 formation, and the succession of the different layers, as exposed 

 naturally, and nearer the surface, or to some extent in perpen- 

 dicular cuts and excavations, there may be found reliable indica- 

 tions of the position of each layer in other places. With the aid 

 of this guide it might be generally known, in advance of all search- 

 ing, and for miles of surface upon which the seeker for marl had 

 never trod, whether and where marl would probably be found, and 

 of what quality, and where there would be none worth working. 



This very thick formation, or bed of many layers of different 

 qualities, as has been stated, has a general dip to the south-east, or 

 down the general course of the river. In the opposite direction, 

 up the river, or as proceeding north-westward, all the layers, (unless 

 running out earlier,) in succession, rise above the level of the river; 

 and consequently, each of these layers, in succession, becomes the 

 upper one at some locality, and is there the first and perhaps the 

 only one to be reached by digging. And as the ancient flood had, 

 by its denuding action, washed away all these raised edges of layers, 

 and so made a new surface approaching to horizontal, it follows 

 that each layer, after appearing as the highest and most accessible 

 at some place, thence thins out as proceeding westward, until that 

 layer disappears, and the next one in order, below, becomes there 

 the highest and most accessible layer. The figure of the following 

 section, though for much the greater part conjectural, will serve for 

 better explanation, and may serve to indicate, either as to this or 

 other beds and localities, how to direct searches for concealed marl, 

 with the best prospect of success, and to avoid the loss of useless 

 examinations. The suppos-ed surface line is designed for the south- 

 ern side of the Pamunkey, and the eocene beds (and overlying 

 miocene also, in part) where exposed nearest to the river. The in- 

 clination of the dip, and also the perpendicular distances, are both 

 greatly magnified in proportion to the horizontal distance, for the 

 purpose of making the successive layers more distinct, and of 

 bringing the whole extent of surface within convenient size. 



