743 



FARMERS' REGISTER— LOWER TERTIARY OF VIRGINIA. 



applying a calcareous marl in which this sub- 

 fitance is peculiarly abundant. In the vicinity of 

 "Williamsburg, almost every variety of the com- 

 mon marl maybetbund; but that which has been 

 obfeserved to produce the most striking effects as a 

 manure, has unifcirmly yielded to chemical exam- 

 ination a comparatively large proportion of the 

 green sand. NVIien therefore, it is in the {)ovver 

 of the farmer to make the selection, such marl 

 should be chosen, as, along with a large propor- 

 tion of calcareous matter in a suitable state of 

 subdivision, contains also ag great an amount as 

 possible of this auxiliary manure. The beds of 

 ehamtt already relerred to, as aboundinii on some 

 estates in this vicinity, p.re peculiarly rich in this 

 ingredient, and are hence, as well as from their fri- 

 able texture, generally selected in preference to 

 fill others. In some of these deposites, as large a 

 proportion as thirty, and in some specimenis forty 

 per cent,, haa boen found; and in cases like this, if 

 we are to trust to the experience of New Jersey, 

 a very marked addition to the fertilizing power of 

 the marl must be ascribed to the presence of this 

 inorredient. 



In alluding thus to the influence of the green 

 eand as an auxiliary manure, the inquiry naturally 

 arises, to which of its ingredients are its meliora- 

 ting effects to be ascribed, or do they arise from the 

 conjoint action of the potash and" oxide of iron 

 which it contains? To this inquirj*, perhaps, it 

 would be premature to attempt to respond. At 

 all events, the rationale of its action cannot be 

 given with that certainty, which in such matters, 

 jt is desirable to attain, A& stated in the fbrm.er 

 conimunication, its components are protoxide of 

 iron, potash andsilex; the latter ingredient appear- 

 ing to act, as it is known to do in maiiy rocks, in 

 the capacity of an acid. In virtue of the potash 

 contained in the green sand, we would naturally 

 infer an agency in ueutra!ir:ing acids similar to 

 that of lime, or its carbonate — and the extent to 

 which the manure possesses this property, must 

 appear still further increased vv'hen v.-e advert to 

 the chemical nature of the protoxide of iron. 



Iron, like most other metallic bodies, combines 

 with oxygen in more than one proportion. These 

 compounds, or oxides as they are termed, are two 

 in number, and in accordance with the general rule 

 adopted by chemists in designating this class of 

 substances, that which contains the least propor- 

 tiim of oxygen, is called the protoxide— that contain- 

 ing the most, the peroxide. The rust" of iron, and 

 the ped coloring matter of ochreous clays and of 

 bricks and tiles, are impure specimens of the per- 

 oxide of iron, Tbe protoxide is never found in 

 an uncombined condition; and such is the avidity 

 with wiiich it imbibes an additional ("[uantity of 

 oxygen, or unites with carbonic and other acids, 

 that it undergoes a rapid change whenever disen- 

 gaged. Hence, under favorable circumstances, 

 a strong neutralizing action m.ight be anticipated 

 from this ingredient of the green sand. We may 

 therefore, for the present, rest our explanation of 

 the agency of this manure upon tlie alkaline pro- 

 perties of these two constituents, the potash and 

 the protoxide of iron. But in sugaestinir this ex- 

 planation, it nuist be freely confessed that, espe- 

 cially as relates to the action of the protoxide of 

 iron, it must be looked upon aa problematical, 

 and requiring for the establishment ot' its truth, an 

 exp^rimer«tal knowledge of the iiitluence of this 



substance upon the growing vegetable, of which 

 nothing has aa yet been positively determined. 



As already indicated, when these inquiries 

 were entered upon, and at the time when my first 

 communication appeared in the Register, the ex- 

 istance of a lower tertiary deposite in Virginia 

 had not been ascertained. The industry of Mr. 

 Conrad had brought to lirrht a formation of this 

 nature in Alabama, and had led to the jirobable in- 

 ference that it might be Ibund in Maryland. 

 Moreover one or two of the fossils obtained from 

 the editor of the Register encouraged the hope 

 that it might be found in our own state. The ob- 

 servations of that gentleman respecting the gyp- 

 seous earth of James River* had appeared some 

 time before, and though nothing positive could be 

 gained from them, in relation to the geological 

 character of the deposite, to which he affixed that 

 name, they threw out the important and saga- 

 cious suggestion, that this earth was the same 

 with the green sand of New Jersey, or at least a 

 substance of analogous character, We shall in 

 the sequel, learn that though geologically the two 

 formations belong to periods which are distinct, 

 the gypseous earth contains a large proportion of 

 that particular ingredient, (the green silicate of 

 iron and potash,) of which the New Jersey de- 

 posite almost exclusively consists. We are there- 

 tore indebted to the editor of the Register, for the 

 announcement of the important fact, that the 

 green sand, or a substance analogous to it, existed 

 in certain localities on the James River. 



Following up the suggestions of geological 

 analogy, alluded to in my first paper, and stimu- 

 lated 1[\v the observations and statements of Mr. 

 Ruffin, I have been enabled bj^ personal inspec- 

 tion, and through the kindness of correspondents, 

 to ascertain with certainty, the existence of a 

 hwsr tertiary deposite, throughout an extensive 

 district of Eastern Virginia, and moreover to deter- 

 mine what is far more important to the agriculture 

 of this region, that the deposite in question com- 

 prises immense strata of green sand, nearly, if not 

 quite, equal in value to that which is in use in New 

 Jersey. The reader, however, is by no means to 

 infer from the existence of the green sand so 

 abundant, both in this lower tertiarj^ and in the 

 New Jersey formation, that the two deposites be- 

 long to the same geological era. I have already 

 stated that the New Jersey green sand, is a se- 

 condary deposite — and of course anterior to the 

 formation here designated as lower tertiary. The 

 shells and other fossils, entombed in the two de- 

 posites are strikingly different, and characteristic of 

 difference of geological antiquity. As it is desira- 

 ble that clear ideas should be entertained, in rela- 

 tion to the distinction here drawn^ I would claim 

 the indulgence of the reader, in presenting such 

 explanations, and illustrations, as are calculated 

 to throw light upon a subject in which, at least in 

 some particulars, all are obviously interested. 



The term primary having been adopted by geo- 

 logists as designating that extensive class of rocks 

 which fi-oni various indications, appeared in gene- 

 ral to have originated^rsf, and which are destitute 

 of all traces of animal or vegetable existence — 

 the title of secondary, was of course appropriated 

 to a class, apparently of nnore recent origin, usu- 

 ally overlying the former, and in which, in many 



"Article "Gypseous Earth," Fflr. Rep:- vol. I. p. 207. 



