668 



FARMERS' REGISTER. 



[No. 11 



which geologists have discovered so many me- 

 morials in oi her regions, and may serve when mi- 

 nutely studied, to throw much light on the physical 

 changes to which this portion of the continent 

 must formerly have been subjected. 



Beneath these beds of gravel, in many places 

 strata of clay occur; but. whether referrable to the 

 same epoch of deposition, cannot as yet. be clear- 

 ly ascertained. Many beds of very argillaceous 

 clay, suited lor the potter and brickmaker, and oc- 

 casional layers of a pure beautiful yellow ochre, 

 may be placed in this portion of the series. 



Other strata of clay and sand of a peculiar 

 character present themselves in many localities 

 beneath the superficial beds. These contain a 

 record of their origin legible to the geologist, in 

 the impressions of shells and Zoophytes with 

 which they are generally filled. On comparing 

 these casts, which m most cases can be easily re- 

 cognized even in their more delicate markings, 

 with the fossils of our Miocene, marl strata, their 

 identity is established, and thus the strata in ques- 

 tion at once take their places in the series of Mio- 

 cene Tertiary deposites. In many parts of Han- 

 over, King William, Henrico, and other counties 

 in its range, these beds of clay are found, usually 

 characterized by a dark greenish gray or brown 

 color, a sulphureous odor, and an astringent taste. 

 On Governor's Hill in Richmond, a stratum of the 

 same kind is exposed; and at this spot, the fossil 

 impressions and other characters above noticed, 

 may be distinctly seen. Like the clays and sands 

 formerly described as associated with the Miocene. 

 these contain sulphate of iron (or copperas,) sul- 

 phate of alumina (or alum,) and sulphur in an 

 uncombined condition. So large a proportion of 

 these substances is sometimes present, as lo render 

 the water obtained from the strata in which they 

 exist, absolutely unfit for use. 



It is to the existence of these materials in the 

 strata, that we are to look for the cause of the dis- 

 appearance of the calcareous matter, in the form 

 of shells, which they once evidently contained. 

 Either of the sulphates above named would exert 

 a rapid decomposing action on the carbonate of 

 lime, of which shells principally consist. The 

 sulphuric acid of the sulphate combining with the 

 lime of the carbonate, thus converting it into gyp- 

 sum, while the carbonic acid would, in great part, 

 escape in the form of gas. That the gypsum is 

 not now discovered in these beds, is an obvious 

 result of the comparative solubility of that sub- 

 stance in water; its continuance in the strata being 

 only possible where a heavy covering of clay ex- 

 cluded the percolating liquid. 



Useless, if not injurious, as these clays are now 

 believed to be when applied to land, there is rea- 

 son to think that they are capable, by a little ap- 

 plication of chemical knowledge, of being render- 

 ed truly valuable as an auxiliary manure. The 

 gypsum into which their enclosed shells were once 

 converted, would doubtless have imparted to them 

 a high agricultural value. Can we not replace.^ 

 not all, some portion of this fertilizing material, bv 

 mingling the clay with the more pulverulent shell 

 marls occasionally found in its vicinity? That this 

 mixture would result in the conversion ofi/a por- 

 tion of the shelly matter info frypsum, there can 

 be no doubt; and where the clay was originally 

 rich in copperas and alum, the amount ofe the gyp- 

 sum thus compounded would be proportionally 



great. Experiments on this subject are well 

 worthy of being tried, not only with the clays 

 here mentioned, but with those of a similar na- 

 ture, which, as already remarked, occur in the 

 more eastern portion of the Tertiary districts of 

 the state. 



Before the amount of gypsum to be anticipated 

 from such a treatment of these materials can be 

 estimated, a chemical determination of the pro- 

 portion of sulphates of iron and alumina must be 

 had, and to this point future analysis might be use- 

 fully directed. 



But though much ol the Miocene marl in this 

 district has been exposed to the destructive chem- 

 ical agencies above explained, much also is found 

 retaining its carbonate of lime in undiminished 

 quantity. 



On the lower levels on their river banks, if ap- 

 pears seldom to have escaped the dissolving and 

 decomposing action of the sulphates, while in the 

 highlands it may usually be found containing its 

 calcareous matter nearly as when first deposited. 

 In King William, Hanover, Prince George, &c, 

 beds are found in the highlands, at some distance 

 from the. rivers. The fossils they contain are 

 identical with those of the marl beds farther east, 

 and the materials with which they are intermixed 

 presenl no peculiarity important to be remarked. 

 Specimens of this Miocene from Hanover, King 

 William and Prince George, exhibit a good per 

 centage of the carbonate of lime, and as might be 

 expected, the strata from which they were taken 

 are usefully resorted to by the neighboring farm- 

 ers. 



As would be. inferred from remarks previously 

 made, the general level at which this marl occurs, 

 is higher than that of the Eocene, and here the 

 promise is held out that this latter, even in the 

 highlands, would be exposed by excavations car- 

 ried to some depth beneath the lower limits of the 

 former. 



In examining the Eocene deposite on the Pa- 

 munkey and James Rivers, the interesting geolo- 

 gical fact was observed of an actual superposition 

 of the Miocene upon it; and on the Pamunkey, 

 the precise point was determined at which the 

 Eocene first makes its appearance above the wa- 

 ter-line, being there overlaid by a. heavy bed of 

 the more recent deposite. This occurs at North- 

 bury, and directly opposite at the plantation of doc- 

 tor Charles Braxton. 



Of the Eocene or lower Tertiary marl. 



The descriptions and facts which will be com- 

 prised under this head, will principally refer to the 

 localises on the Pamunkey and James Rivers, to 

 whicfl especial observation has been directed. At 

 the same time that, their value, as applying to the 

 Eopene district generally, ma}' be regarded as being 

 sufficiently established by general geological anal- 

 ogies, as well as such observations upon other 

 portions of the region, as the present early stage 

 of the inquiries has allowed me an opportunity 

 of making. No region of eastern Virginia holds 

 out more certain promise of reward to future in- 

 vestigation, and none will reap from the research 

 more lasting and important benefits. 





