420 



FARMERS' REGISTER, 



[No. 7 



be forgotten. Or if perchance } he strikes out some 

 new discovery, his name may be recorded in the 

 annals of the science, and recited annually by pro- 

 fessors in their introductory lectures; but solar as the 

 great world of mankind is concerned, he is yet ut- 

 terly unknown to fame. But let him once turn 

 his attention to practical affairs — be no longer a 

 man of speculation, but ol" action — and how soon 

 the obscure philosopher is converted into a promi- 

 nent public benefactor. His lame, no longer con- 

 fi icd to mere men of science, in this reading age 

 E03n pervades society, and becomes emphatically 

 popular. Why else is itthat the scientific fame of 

 Franklin and Davy is so much more extensively dif- 

 fused than that of Priestly, Cavendish, Lavoisier 

 and others, who, equally eminent among men of 

 science, have yet failed to make any impression 

 on the popular mind? The lightning rod of Frank- 

 lin, and the safety lamp and Agricultural Chemis- 

 try of Davy, have so connected them with the 

 common affairs of lite, that they can never be for- 

 gotten; and each of them may be said with truth 

 to have erected for himself a monument more du- 

 rable than brass. The agricultural community has 

 reason to congratulate itself that these splendid ex- 

 amples are not likely to be lost on the zealous and 

 indefatigable professor of chemistry in the Uni- 

 versity of William and Mary. 



Connected with the subject of the green sand 

 formation, there is a most interesting inquiry but 

 slightly noticed by Professor Rogers, to which my 

 attention has been frequently turned, and of which 

 I have yet seen no satisfactory solution. I allude 

 to the remarkable fact, almost universally observ- 

 ed, of the disappearance of calcareous matter near 

 the surface of our marl beds. I propose in this 

 communication to offer some conjectures on the 

 causes and effects, in an agricultural point of view, 

 of the chemical changes which this deposite has 

 evidently undergone. 



So far as my information extends, this fact is 

 alwa3 T s observed near the surface of beds of blue 

 marl. The upper stratum consists invariably of 

 what at first sight appears to be blue clay, but 

 when more nearly examined is found to be com- 

 posed principally of a silicious substance, through 

 which are interspersed distinct impressions of 

 shells, and numerous shining particles, (according 

 to Protessor Rogers) of mica, but which I take to 

 be seleniie or pure gypsum. I have occasionally 

 found in these beds what at first appeared to be 

 an actual shell fish, with both shells and the hinge 

 seemingly perfect; yet so entirely destroyed was 

 the hard substance of which it was originally com- 

 posed, that it would yield to the slightest touch, 

 and the application of the strongest acids could 

 not detect the presence of the least portion of the 

 carbonate of lime. What has become of this cal- 

 careous matter? This is an inquiry equally inter- 

 esting to the geologist, and to the agriculturist, and 

 it is surprising that no satisfactory solution of it 

 has yet been given, or even attempted. In your 

 Essay on Calcareous Manures, second edition, 

 page 49, speaking of a deposite which had once 

 been a bed of fossil shells, you say: "Not the. 

 smallest portion of calcareous earth can be found 

 — and the gypsurn into which it must have been 

 changed, (by meeting with sulphuric acid or sul- 

 phuret of iron) has also disappeared in most 

 places," &c. — and Professor Rogers in his arlicle 

 re-published in the Appendix to the Essay on 



Calcareous Manures, uses the following language: 

 "Besides a considerable proportion of green sand, 

 it contains, in addition to the crystalized gypsum, 

 a notable amount of this substance in a sub-divi- 

 ded state, and seemingly occupying the place of 

 the shells, which were lormerly present, and have 

 been decomposed under the chemical agency of 

 some substance which filtrated in solution through 

 the mass'" — (page 115.) In the article on gypseous 

 earth published by you in the Register as early as 

 September 1S33, the fact of the disappearance of 

 calcareous matter from beds formerly composed of 

 lossil shells is mentioned, and the difficulty of its 

 explanation very clearly stated. That sulphuric 

 acid is the agent in effecting this remarkable 

 change, there can be no doubt; but whence is it 

 derived? And what new combinations have been 

 Ibrmed? These questions are not suggested by a 

 mere spirit of speculative curiosity, but .are of high 

 practical importance, inasmuch as upon their so- 

 lution depend the chemical character of this sub- 

 stance and its value, as a fertilizing agent, to the 

 agricultural community. 



In prosecuting this inquiry, I shall proceed on 

 the supposition that the beds of gunpoivdcr marl 

 of New Jersey, containing the green sand, are 

 similar to our beds of blue marl in Virginia; the 

 descriptions given by Professor Rogers of the New 

 Jersey deposites agreeing precisely with those that 

 I have examined in Virginia. I take it for granted, 

 also, that no accurate analysis has been made 

 (because none is reported) of the substance called 

 gunpowder marl, the analysis of Professor Rogers 

 having been confined to one of its ingredients," the 

 green sand. 



The following theory, which I offer without any 

 great degree, of confidence m its correctness, is at 

 least not destitute of plausibility, and is certainly 

 strongly sustained by some striking facts connect- 

 ed with this deposite. Suppose the presence of 

 sulphuretted hydrogen gas, generated by the de- 

 composition of the animal matter of the shells, or 

 of the fish originally inhabiting them. Or more 

 probably, it may be an exhalation from the wet or 

 marshy places, in which these beds are usually 

 found. The writers on mineralogy in giving the 

 geognostic situation of sulphuretted hydrogen, 

 say that "it rises from sulphureous springs, also 

 from marshy places, and is met with in mines" — 

 or it may probably be produced by some chemical 

 change effected in the earth with sulphurct of iron, 

 or of antimony, from both of which substances 

 chemists are in the habit of procuring sulphuretted 

 hydrogen. But however generated, the existence 

 of sulphuretted hydrogen gas, in the low ravines in 

 which the marl beds are usually found, is extreme- 

 ly probable. This gas is composed of hydrogen 

 -and sulphur, in certain proportions. A small por- 

 tion of sulphuric acid is also supposed to enter into 

 its composition. It possesses decidedly acid pro- 

 perties, for it reddens litmus paper, and forms 

 sails with alkalies. It is hence, sometimes called 

 hydro-sulphuric acid. (Turner's Chemistry, 252.) 

 Its elements may easily be separated from one 

 another. Thus, on putting a solution of sulphu- 

 retted hydrogen into an open vessel, the oxygen 

 absorbed from the air gradually unites with the 

 hydrogen of the sulphuretted hydrogen, water is 

 formed, and sulphur deposited. (Ibid.) It seems 

 therefore that the natural effects of the formation 

 and disengagement of sulphuretted hydrogen gas, 



