1835.] 



FARMERS' REGISTER. 



39 



incumbent soil is ferruginous, it veiy generally hap- 

 pens that the shells are bound together by an argillo- 

 ferruginous cement extremely hard, which unfits them 

 for use not only in this respect, but also by substituting 

 for the calcareous ingredient which they originally con- 

 tained a predominating constituent of oxide of iron, 

 which cannot be beneficial to the soil. 



"It must be borne in mind, however, that this sort of 

 disnaturing of the shell-inarl is most generally confined 

 to the upper portions of the deposite. Hence, if in 

 the search after marl, those silicious or ferruginous in- 

 crustations are met with, they should always be re- 

 moved to ascertain the nature of the material beneath. 

 There is a very remarkable example of a thick coat of 

 silicious incrustations covering very excellent marl, on 

 the estate of William Carmichael, Esq. on Back Wye, 

 Queen Ann's county. 



"As to the fossil constituents of the shell-marl dc- 

 posites on the Eastern Shore of Maryland they are 

 very various. Some are principally composed of 

 oyster shells, others principally of scallop, some 

 again principally of clam, and in others nearly the 

 whole bed consists of perna, commonly known by the 

 name of pearl shell. These last furnish decidedly the 

 best marl. The perna is a broad, thick shell, some- 

 what in the shape of a large oyster, of a white pearly 

 appearance, peeling off in thin laminae that are very 

 soft and friable. When exposed to the atmosphere for 

 a short time it falls into an almost impalpable dust, con- 

 sisting essentially of carbonate of lime. This shell 

 occurs in most of the marl beds of the Eastern Shore, 

 but more especially in those of Talbot county, and as 

 already stated, at the head of Reed's creek, in Queen 

 Ann's county. 



"The quality of the marl is also greally influenced 

 by the nature of the shells that compose it. It was 

 stated in the former report, and may be repeated here, 

 in illustration of what has to be said under the present 

 head, "that those beds which consist principally of 

 clam shells, usually associated with numerous varieties 

 of othersmaller bivalve and univalve shells, containing 

 at the same time very little admixture of foreign in- 

 gredients, yield a marl which exhibits its beneficial 

 effects upon the soil in a very short time; because the 

 calcareous particles are derived from shells which are 

 very prone to disintegrate when exposed to the atmos- 

 phere. Marl beds, composed entirely or principally of 

 oyster shells, are much less valuable, because of the slow 

 disintegration and decomposition of this species of 

 shell. Scallop shells resist such decomposition still more 

 obstinately than do oyster shells, and when they occur, as 

 they have been observed to do, in extensive beds firmly 

 agglutinated by an argillo-ferruginous cement, they are 

 useless in all soils, and may be positively injurious to 

 some." 



"It follows then, that the nature of the material in 

 the shell-marl deposites must be ascertained first in re- 

 ference to the species of shells which it encloses, and 

 their admixture with foreign ingredients, as clay, sand, 

 gravel, &c. This can be done by a simple inspection 

 aided by such experience and knowledge as can be 

 acquired without any difficulty. But a more impor- 

 tant consideration relates to the composition of the marl, 

 and especially to the relative proportions of its three 

 principal constituents, namely, carbonate of lime,alu- 

 mine and silex. To ascertain this recourse must be 

 had to a chemical analysis. The proportion of calca- 

 reous particles is doubtless generally the most impor- 

 tant fact to be determined; but it sometimes becomes 

 equally important to ascertain the proportions of alu- 

 minous and silicious particles; for, one of the advan- 

 tages, and not an inconsiderable one, in the application 

 of marl is its use in ameliorating the mechanical con- 

 dition of the soil, and these ingredients are eminently 

 serviceable in this way. 



"From what has already been said, it will readily be 

 perceived that great variety must also necessarily pre- 

 sent itself in the chemical composition of the marl in 



its different localities. So far as experiments havcbeei> 

 conducted, it has been found that the proportion of cal- 

 careous particles varies from 20 to CO per cent.; that of 

 aluminous from 10 to 20 per cent, that of silicious in- 

 gredients from 30 to 50 per cent. 



"It is doubtful whether any directions could be given 

 which would enable those unpractised in chemical op- 

 erations and manipulations to ascertain with any de- 

 gree of accuracy the relative proportions of these con- 

 stituents of the marl. This is a subject which must be 

 submitted to some analytic chemist; and it is the duty 

 of the geologist to satisfy inquiries of that sort when- 

 ever called upon for that purpose. On the proposed 

 geological map of the state, it is contemplated to ex- 

 press the composition of the marl in the principal local- 

 ities that will be laid down; and by extending the ta- 

 ble exhibiting the chemical analyses of these marls, to 

 all such as can be conveniently procured, a mass of in- 

 formation will be collected that will in some measure 

 supersede the necessity of any further experiments. 



Though the words of the last three paragraph?, 

 if very strictly construed, may be maintained to 

 be correct, yet they will probably convey a very 

 different, and as we think, an erroneous impres- 

 sion to most readers. It may be readily conceded 

 that no "directions could be given which would 

 enable those unpractised in chemical operations 

 and manipulations, to ascertain with any degree 

 of accuracy the relative proportions of these con- 

 stituents of marl 1 ' — if "these constituents" are to 

 be separated with absolute accuracy, as arranged 

 in the table, of marls analyzed (p. 61,) under the 

 heads of "silica, alumina, lime, carbonic acid, oxide 

 of iron, potassa, and water." To execute this 

 separation correctly, would indeed require not only 

 the labors of an "analytic chemist' 1 but of one of 

 a very high order of talent. If all Dr. Ducatefs 

 analyses of calcareous marls were as carefully and 

 accurately made, he has gone through a most la- 

 borious undertaking, and to very little purpose. 

 But if this array of scientific terms and arrange- 

 ment had not been brought forward, and served 

 to create apparent difficulty, and the operation is 

 confined to what is important and necessary to the 

 farmer, the very opposite of the above opinion 

 might be truly expressed, viz: that any person of 

 ordinary intelligence may easily learn to analyze 

 his own calcareous earths — and for all useful and 

 practical purposes, with as much correctness as the 

 analytic chemist. Farther — the results so to be 

 obtained, would be even more correct than those 

 of the author's analyses, on account of a delect 

 in his mode of examination, which will presently 

 be noticed more particularly. Such directions (lor 

 example) as are given in the Farmers' Register, 

 Vol. I. p. 609, if attended to, will enable any one 

 to analyze marl so as to know the amount of cal- 

 careous matter — and if desired, the proportions of 

 silicious sand and aluminous earth, or pure clay, 

 are as easily found. The two latter ingredients, 

 however, would seldom require more nicety of ob- 

 servation than a glance at the residuum, as 

 shown after removing the calcareous parts. The 

 proportion of oxide of iron is still less impor- 

 tant — (at least for any purpose yet known;) of "wa- 

 fer" as a chemical ingredient of calcareous marl, 

 our ignorance is readily confessed — but at all 

 events, its presence cannot affect the value of the 

 manure, except in adding to its useless weight. 

 The column for potassa (potash) is a blank 

 throughout the whole list of calcareous marls (be- 

 ing found only in the green sand, and not in cal- 



