352 MESOZOIC FLORAS OF UNITED STATES. 



On the gradual elevation of this fresh-water valley, with its included beds of 

 clays, etc., the Delaware River cut its way tlu-ough the latter nearly to the south- 

 eastern rise, and was then deflected along the base of these first elevations of the 

 bounding anticlmal, in a southwest direction. Thus is accounted for the apparently 

 singular phenomenon of the great bend of the Delaware River near Bordentown. 

 For after penetrating the liigh ranges of the Blue Mountains, it remains to be turned, 

 apparently, in a level country of sands and clays. 



We must suppose the coast line to have been not far from the southeastern 

 base of this anticlinal, and that a subsequent submergence brought the marine 

 deposits near to the margin of the fresh, and gave the latter the southeast dip 

 visible at the section of the Pea shore. I have not yet been able to ascertain the 

 relative position of the margins of these beds, nor the nature of those that conceal 

 the supposed anticlinal. A system of borings at a distance of two or three miles 

 from and parallel to the Delaware would do much toward explaining this point. 

 It is to be hoped that this may be undertaken by the present State Survey, under 

 Professor Cook. 



At the present time the cities of Alexandria, Washington, and Baltimore stand 

 upon its deposits, and Philadelphia is probably underlain by its margin, as well as 

 the adjoining margin of the gneiss. Indeed, the location of the prominent cities 

 of the Atlantic States appears to have been determined by the fine sites and water- 

 powers offered by the junction of the high rolling country of the gneiss formation^ 

 and the lower and more level regions of the supposed Neocomian, Cretaceous, and 

 Tertiary. Where the gneiss strikes the ocean is situated our greatest seaport. 

 New York. Trenton, Philadelphia, Wilmington Baltimore, Washington, Alexan- 

 dria, Richmond, Raleigh, Columbia; and Milledgeville, Georgia, are all on this line 

 of juncture. The elevated gneiss hills furnish healthy and beautiful residences, the 

 fall furnishes water power, and the lower level, water communication, and a light 

 soil most suitable for gardening and the production of provisions for these centers 

 of population. 



At the meeting of the Boston Society of Natural History of May 19, 

 1875, Prof. W. B. Rogers presented some "Geological Notes," one of 

 which was "On the Gravel and Cobblestone Deposits of Virginia and 

 the Middle States,"" which is remarkable from the fact that Professor 

 Rogers here clearly distinguishes the more superficial gravels belonging 

 to the Pleistocene beds, now called the Columbia formation, and the 

 Pliocene beds, known to modern geologists as the Lafayette formation, 

 from the Cretaceous gravels belonging to the Older Potomac. Toward 

 the close of the paper he enters somewhat into the general discussion of 



Proc. Boston Soc. Nat. Hist., Vol. XVIII, May 19, 1875, pp. 101-106; Geology of the Virginias, pp. 

 707-713. 



