630 



FARMERS' REGISTER. 



[No. 10 



empty, and we may, therefore, conceive, that as I may be observed, each distinguished by the pre- 

 the matter ot the shell in an extensive bank of dominance of one or more species, and the order 



Charaaa is gradually dissolved, the water charged 

 with carbonate of lime enters the cavities, and 

 slowly deposites the carbonate mixed with fine 

 particles of clay and sand. Thus by degrees the 

 cavities are filled. In the mean time the shell 

 disappears, frequently leaving on the surface ol 

 the cast a chalky covering, like the decomposed 

 inner film of shelly matter. In support of this ex- 

 planation it. may be added, that in many casts 

 beautiful crystals of carbonate of lime are found, 

 forming a portion ot' the cast, and having the ap- 

 pearance ol' Dog-tooth Spar. In some cases the 

 shelly matter appears to have been dissolved, and 

 its place supplied by the crystallized carbonate, 

 encrusting the earth formerly contained within the 

 shell. Sometimes, too, a thin film of oxide ol 

 iron surrounds the cast, showing very distinctly 

 all the markings of the inner surface of the shell. 

 In many localities, presenting a series of beds dif- 

 fering in composition, the shells will be found per- 

 fect in some of them, while in others immediately 

 above or below, only casts remain. Thus at the 

 College mill, about one mile from Williamsburg, 

 the upper Ibssiliferous layer is a yellow silicious 

 sand, containing peiiect shells. Below this is a 



of superposition of these beds frequently continues 

 without interruption for some distance. It does 

 not appear, however, that in localities remote from 

 each other, the arrangement of the shells is al- 

 ways alike, although in many instances there ap- 

 pears to be a striking correspondence. In a major- 

 ity of cases in the neighborhood of Williamsburg, 

 the upper layer is composed principally of Chama 

 congregata. In many localities also, the large 

 Pectoris mingled with Ostrea Virginica occupy the 

 highest place. But generally, the same shell re- 

 appears as a predominant constituent of one or 

 more of the subjacent beds; and such is the di- 

 versity of arrangement, even in the places but a 

 lew miles distant, that it is obvious that no general 

 order of the succession exists. Thus, in a range 

 of three miles we find Perna maxillata in some lo- 

 calities in the lowest stratum of dark blue argilla- 

 ceous sand; in others, forming an upper, or even 

 the highest layer of the series. At Waller's mill, 

 three miles from Williamsburg, this fossil overlies 

 the other shells; whereas at the College mill, as 

 already stated, it forms a part of the lowest visible 

 stratum. 



With the view of conveying more precise ideas 



brown ferruginous clay, filled with the most beau- j of the disposition of the fossils in this region, we 

 tiful casts of Chama, Pectunculus, Turritella, &c. annex the following details in relation to some of 

 The shelly matter has entirely disappeared, and J the more important localities, which have been 

 the casts lie loosely in the cavities produced by j minutely examined, 

 the removal of the shells, entirely distinct from i King's mill, one of the most interesting fossil lo 



each other, and covered by a film of oxide of iron 

 The layer beneath, consisting of bluish green si- 

 licious clay, is full of well preserved Pectens, Per- 

 nas, and a variety of other shells. 



In general, the various species of shells are 

 found associated in colonies or groups, but as in 

 the case of banks of recent shells, these colonies 

 contain many scattered specimens, differing from 

 the general contents of the group. The two spe- 

 cies of Chama, the C. congregata and C. corticosa, 

 which are found in almost every deposite of shells 

 in this region, in many cases form extensive, beds 



calities in the neighborhood of Williamsburg, is 

 situated on the north bank of James river, about 

 twenty-five miles from its mouth. The cliff in 

 which the shells appear is abrupt, and has a 

 height varying from twenty to forty-five leet above 

 the water. The strata of shells extend along 

 the river with slight interruptions, when the cliff 

 sinks nearly to the level of the water, for a dis- 

 tance of between two and three miles, and they 

 are found in a somewhat similar order of superpo- 

 sition for some distance inland. Their general di- 

 rection is horizontal, but the outline of any one 



with a very small admixture of other genera. The stratum is frequently very irregular, the surface ri- 

 best agricultural marl, of a purely calcareous na- J sing and falling with a steep inclination. This 

 ture. which is used in lower Virginia, is derived j irregular outline is particularly remarkable with the 



from these beds of Chama, the friable texture of 

 the shell upon exposure to the air, rendering this 

 species of marl more easy ol application to land, 

 and more prompt in its ameliorating effects. Cras- 

 satella? often form an extensive deposite, and the 

 large Pectens occur in continuous layers of con- 

 siderable depth and extent. The different species 

 of Area, Artemis Crepidula, &c. present a similar 

 arrangement. Even those shells which are of 



beds of Chama, which are very thick at some 

 points, and then fine out rapidly and again ex- 

 pand. 



This deposite of shell is covered to the depth of 

 from four to six feet by a brownish yellow sand, in- 

 termixed with stripes of clay. Beneath this a 

 thin layer of about one foot, of very argillaceous 

 and ferruginous clay of a red color. This rests 

 upon a few inches thickness of gravel, consisting 



comparatively rare occurrence, are usually found j of water-worn quartz, rarely larger than a pea. 



little groups. Thus the Isocardia fraterna is 

 found, to the extent of a dozen or twenty, closely 

 packed together. This gregarious assemblage of 

 shells of the same species is what would naturally 

 be anticipated in the absence of violent agencies 

 during or after their deposition, and furnishes an- 

 other very striking proof of the comparatively 

 tranquil condition of the sea or estuary r in which 

 they were allowed to accumulate. 



Disposition of the fossils. 



In nearly all the verlical sections of the depos- 

 ite we are now describing, a series of beds or strafa 



Beneath this is a layer, from one to two feet thick, 

 consisting of yellow sand, containing a great deal 

 of the green or chloritic sand, arranged in narrow 

 stripes. Next follows a layer of the same sand, 

 containing principally Chama and Venus defbrmis. 

 This is from two or three feet in thickness. Im- 

 mediately below is a stratum consistingalmost ex- 

 clusively of Chama, with a few Area centenaria, 

 &c. This stratum, varying from three to four feet 

 in thickness, is a mass of compacted shells, with 

 but little earthy matter intervening. The earthy 

 matter contains a very large proportion of the 

 chloritic sand. The next stratum is composed 

 chiefly of large Pectens. and has a thickness of 



