1835.] 



FARMERS' REGISTER, 



669 



Description of the Eocene strata of the Pamun- 

 key. 



Rising above the. water-line at Northbury, the 

 upper surface ot' the deposite is seen ascending 

 with a very gentle slope, as it extends higher up 

 the river, until at Newcastle it attains an elevation 

 of about 25 feet above medium tide. Beyond this 

 point, with slight undulations in its outline, it con- 

 tinues with but little general deviation of height 

 from the water-line to near its termination at the 

 junction of the North and South Anna, where it 

 dips or thins out until lost immediately on the. 

 verge of the coarse sandstone, which there, for 

 the first time, makes its appearance in massy 

 form. The deposite appears on both sides of the 

 river wherever the flats do not intervene, and at 

 the base of the second level, corresponding in po- 

 sition to its place in the river cliffs in the same vi- 

 cinity. 



On the south side of the river, the deposite has 

 been particularly examined, at Northbury, Hamp- 

 stead, Retreat, Washington Basset's, Walker 

 Tomlin's, Mrs. Ruin's, Mr. Roane's and Mr. 

 Wickhams's, where it terminates. Specimens 

 have been collected from other localities, either on 

 the river or at the base of the second l«vel: on 

 the north side, at Chericoke, captain Hill's, Mr. 

 Nixon's, Piping Tree, Newcastle, Dr. Braxton's 

 and Mr. Fox's. Specimens also from various 

 other points on, and remote from the river, have 

 been procured, and thus a somewhat minute ac- 

 quaintance with this portion of the Eocene tract 

 has been attained. Towards the southern boun- 

 dary of the deposite, the following arrangement of 

 strata occurs, commencing at. the top. 



1st. A stratum of greenish yellow earth con- 

 taining no shells, but numerous traces or casts of 

 them, plainly showing that shells were at one 

 time embedded in the mass. Sulphate of lime or 

 gypsum occurs in crystals sometimes of conside- 

 rable size, interspersed throughout this stratum, 

 which is principally made up of coarse silicious 

 sand, blended with granules of green sand or sili- 

 cate of iron. The thickness of this bed is varia- 

 ble ; at Chericoke and Hampstead it is about two 

 leet; at Retreat from four to five. 



2d. Beneath this lies a layer of dark greenish 

 blue or browc earth, which when dried, generally 

 falls to pieces, and is discovered to consist mainly 

 of coarse silicious sand, and green sand, together 

 with shells generally in a broken condition. The 

 shelly matter is sometimes entirely wanting, 

 though occasionally it composes a large portion of 

 the mass. At Hampstead, the. calcareous ingre- 

 dient exists in large proportion and in\a finely di- 

 vided state. Fiequently, one or more thin layers 

 of the oyster shell peculiar to the lower Tertian- 

 region occurs in the body of this stratum* a fact 

 remarkably exemplified at Piping Tree, and for 

 nearly a mile further clown the river, where the 

 layer of shells forms a hard rockey shelf laid bare 

 at low tide, and presenting large and perfect spe 

 cimens of the fossil oyster, in the midst of the 

 greenish stratum just described. 



At Chericoke the stratum rises to about four feet 

 above the water, and as ascertained by digging, 

 descends to seven feet below the river shore. 



Higher up the stream, these strata attain a great- 

 er elevation, and subjacent beds not apparent at 

 either of the points above described, come gradu- 



ally into view. In these localities we usually 

 find, 



1st. A layer of dark grayish green or grayish 

 brown color, containing multitudes of shells, gen- 

 erally in a perfect state; the fossil oyster shell al- 

 ready referred to abounding chiefly in the upper 

 part of the stratum. Beneath this, but frequently 

 separated by no distinct line of demarkation, we 

 find, 



2d. A layer of darker hue, containing less shel- 

 ly matter, and the shells chiefly of the smaller 

 kinds; and 



3d. A stratum of the same appearance, in 

 which no calcareous matter can be discovered. 



All these strata contain a large portion of the 

 green sand. In the upper and lighter colored 

 beds, the granules of this substance are very ob- 

 vious to inspection, resembling in size and color 

 the grains of gunpowder, and giving when bruised 

 a bright green stain. In .the lower beds they are 

 more minute, and being intimately mingled with 

 the other materials present, are not readily recog- 

 nized, excepting by the general greenish charac- 

 ter of the mass. These beds also contain a great 

 deal of Mica in fine sparkling scales. Of the 

 depth of these strata below the level of the. river 

 nothing definite is known, no extensive excava- 

 tions having yet been made. At Mr. Wickham's 

 they are found to rest upon a layer of large peb- 

 bles, but this basis is perhaps not co-extensive 

 with the deposite. lower down the river. 



When the upper bounding surface of the Eo- 

 cene is even and uniform, it is always marked by 

 a fhin layer of black pebbles, upon which there 

 usually rests a bed of olive colored earth, or of 

 friable white clay — and in some cases, both these 

 strata, the olive colored being next the Eocene. 



This olive earth is of a fine texture, containing 

 but little gritty sand. Here and there a shark's 

 tooth in a decomposed condition, or the impression 

 of a shell may be discerned. The white stratum 

 abounds in casts, but never presents the shells 

 themselves. It shows a light, trace of gypsum, 

 but in neither of these beds does there exist any 

 carbonate of lime. From the character of the or- 

 ganic impressions they contain, they clearly refer 

 themselves to the Miocene formation. 



In some places on the river, particularly where 

 the upper bed of the Eocene contains gypsum, as 

 at a point a little below Piping Tree, a thin layer 

 of ferruginous rock abounding in casts occurs im- 

 mediately in contact, with the Eocene; this also 

 is to be placed among the strata of the Miocene. 



A more distinct conception of the order and ex- 

 tent of the strata of both the Tertiary divisions, as 

 they occur at different points along the river, will 

 be obtained from the following summaries derived 

 from observation. 



On the north bank of the river in a cliff about 

 half a mile below Piping Tree, the beds taken in 

 a descending order are, 

 Miocene. — 1. White friable sandy clay, 

 containing fossil impres- 

 sions, 10 feet. 



2. White sandy marl with bro- 

 ken shells, i 



3. Ferruginous stratum abound- 

 ing in casts, and occasion- 

 ally containing the shells 

 themselves, A 



1 Thin band of black pebbles. 









