1835.] 



FARMERS' REGISTER 



631 



from one to two feet. Below this is another dense 

 stratum of Chama, together with Area eentenaria, 

 Panopea reflexa, &c. and also very rich in the 

 green sand. Thickness, from four to six feet. 

 Then follows a second layer containing Pec tens 

 with Ostrea compressirostra, one foot in thickness. 

 A third stratum in which Chama predominates, 

 follows next, in thickness from two or three feet, 

 and at the base of the cliff is a layer containing 

 Pectens, Ostrea compressirostra, &c. from four to 

 five feet in thickness. 



Thus through a height of more than twenty 

 feet in some places, the cliff consists principally of 

 shells, of which there are a great many species be- 

 sides those mentioned as predominating in the 

 several beds. On the extensive contiguous estates 

 of King's mill and Littletown, these shells are 

 largely used as a manure: and for this purpose the 

 first and seconds beds of Chama are preferred on 

 account of the immense amount of calcareous 

 matter, and the large proportion of green sand 

 which they contain. Judging from the occasional 

 appearance of bluish green clay on the line of the 

 beach, and in some places immediately at the base 

 of the cliff just described, it is highly probable 

 that a continuous stratum of this substance lies 

 beneath the other beds throughout the whole extent 

 observed. A horizontal bed of yellowish clay ex- 

 tends for some distance along a lower portion of the 

 cliff, in which there are no fossils; running within 

 a few feet of its upper edge, and beneath this bed, 

 and parallel to it, is a thin layer of the iron ore 

 former]} described. At the foot of this cliff ap- 

 pears the underlying stratum of clay. 



Description of the cliffs at Yorktown on York 

 River. 



The elevation, abrupt form, and peculiar struc- 

 ture, of the, cliffs at this point, and for some dis- 

 tance, both above and below, render it an interest- 

 ting spot to the geologist. A dry and ample 

 beach, uninterrupted by creeks or inlets for several 

 miles, affords a ready access to the banks, while 

 the river's edge, strewed with fossils which have 

 fallen from the cliff, exposes a considerable variety 

 of interesting specimens. Immediately at York, 

 the river is only three eighths of a mile in width, 

 but both above and below it expands to a breadth 

 six or seven times as great. 



At Wormley's creek, about two miles below 

 the town, the cliff about to be described begins; 

 but from this point, down to the extremity of the 

 peninsula, the banks are uniformly flat and low. 

 The cliff here consists at bottom of a bluish sandy 

 clay, containing immense numbers of Turritella 

 alticosta, Cytherea sayana, and many small Uni- 

 valves, over which lies a layer of brownish yellow 

 sand, with very few shells, and those chiefly Nu- 

 cula limatula, and a tew other species. To this 

 succeeds a stratum composed almost entirely of 

 Crepidula costata, so closely packed together, as 

 to leave little space for sand or other earthy mat- 

 ter. The whole is covered to a variable depth by 

 a stratum of coarse sand of various strong tints, 

 and evidently highly ferruginous. The elevation 

 of the cliff increases, and the nature of its con- 

 tents gradually changes in approaching York. 

 The lower stratum disappears entirely af.er con- 

 tinuing for something less than half a mile, pre- 

 vious to which, however, its fossil contents are 



changed; the layer of the Turritella? being re- 

 placed by Crepidula closely packed together. Cre- 

 pidula stills runs on horizontally above, and the 

 intermediate stratum is now densely filled with 

 Pectens, Venus deformis, Ostrea, and a great va- 

 riety of small shells frequently connected together, 

 so as to form hard masses of considerable size. 

 Still higher up the river the deposite assumes the 

 character of successive layers composed of com- 

 minuted shells, connected together so as to form a 

 porous rock. These fragments are generally so 

 much rubbed and water-worn, as to render it im- 

 possible to ascertain the species of shells of which 

 they once were portions. Many small shells, and 

 occasionally large ones, particularly Pectens, are 

 found mingled with the other constituents of the 

 rocks; and in some places thin layers of shells, 

 such as Venus and Crepidula, intervene between 

 the adjacent strata. The height of this fragmen- 

 tary rock amounts in some places to forty feet. In 

 most places it has a highly ferruginous aspect, 

 though this is not invariably the case. Frequently 

 shells of considerable size, such as Lucina, ano- 

 donta, are seen coated with, or entirely changed 

 into crystalline carbonate of lime, firmly cemented 

 in the mass. The texture of the rock is various, 

 at some points admitting of being readily excava- 

 ted by the pick and spade, so as to form caves 

 which have been occasionally used by the inhabi- 

 tants; in other places exhibiting a hard and semi- 

 crystalline structure, and having the compactness 

 of some forms of secondary limestone. The lower 

 portion of the cliff, having less cohesion than the 

 rest, has been scooped out by the action of water, 

 so as to give il occasionally an impending attitude. 



Above the town, the stratum of fragmentary 

 rock becomes much thinner, being now reduced to 

 about ten or twelve feet. A stratum of yellowish 

 argillaceous clay, abounding in Artemis acetabu- 

 lum, Madras, and other large shells, lies immedi- 

 ately beneath the rock; and lower still, appears 

 the stratum of bluish clay, filled with Nucula Li- 

 matula, several species of Fusus, and various other 

 fossils. 



A narrow layer of iron ore extends along the 

 cliff, with occasional interruptions, at a small dis- 

 tance above the fossiliferous strata. 



This fragmentary rock continues in a narrow 

 band, with some interruptions, for about a mile 

 and a half above York. Beyond this point it is 

 met with chiefly in detached masses. Extensive 

 beds of shells, similar to those which appear at 

 York, come to view in the vicinity of Bellefield, 

 and line ihe shore for a distance of about three 

 miles. These beds rest on the usual stratum of 

 sandy clay, and are in some places, as already 

 described, covered by a stratum of the same sub- 

 stance. At a still remoter point, about six miles 

 above York, on Jones's plantation, a porous rocky 

 mass occurs, overlying the stratum of shells in a 

 thin and interrupted layer. Though very similar 

 in appearance to the fragmentary mass before de- 

 scribed, and evidently at one time composed of 

 portions of shells, it is almost devoid of any trace 

 of carbonate of lime. It appears to consist of si- 

 lex, slighty tinged with oxide of iron: approaching 

 in its porous character and harsh gritty texture, to 

 the nature of the burr stone of France. Associa- 

 ted with this, is a more compact rock, containing 

 some carbonate of lime, much silex, and exhibit- 

 ing very perfect casts and impressions of Pectens, 



