232 CALCAREOUS MANURES— APPENDIX. 



losophical Society of Philadelphia in 1835, and again in the first report 

 of the geological survey of Virginia, the material, parts of the above state- 

 ments are re-asserted, in substance, and nearly in the same words. These 

 statements and opinions were received, when announced, as undoubted, 

 and they have not since been questioned in any publication ; nor have they 

 since been either confirmed by any additional proof or testimony, nor have 

 they in direct terms been modified or retracted by their author. Yet the 

 correctness or incorrectness of the assertion of such abundance and general 

 diffusion of green-sand in the miocene marls of Virginia is a matter of great 

 interest — and, in its bearing on the application of marl and the rationale of 

 its operation, of great importance to agricultural improvement. It is certain 

 that to this day, many proprietors consider that their marls are peculiarly va- 

 luable because of the supposed large proportions of green-sand therein — 

 such opinions being founded either on the publications, or, with still more 

 confidence, upon the personal examinations and verbally expressed opinions 

 of the state geologist. 



My own personal examinations of marls in place, and analyses of speci- 

 mens of other beds, have been very extensive ; and my attention has been 

 given especially in regard to this point to sundry specimens, including 

 several of the particular bodies of marl which it is understood that Pro- 

 fessor Rogers had pronounced to be very rich in green-sand— containing, 

 say, 20 to 30 per cent, of the black granules so called. I have found 

 some green-sand (but generally in very small proportion,) in nearly all the 

 specimens examined particularly for this substance ; and believe that Pro- 

 fessor Rogers was correct so far as inferring that it is a very frequent 

 ingredient. And for the first observation of this curious and interesting 

 fact he is justly entitled to the entire credit. To such extent as green-sand 

 is present, and according to the manner of the operation of that earth, 

 (whatever that may be,) the green-sand in the miocene marls must be 

 effective and useful. But whether such effect be of any distinguishable 

 and appreciable value, or not, depends on the quantity and proportion of 

 green-sand in the marl ; and, so far as all my experience and observation 

 enable me to judge, I cannot but believe that the above stated estimates 

 of quantities and proportions of green-sand are greatly exaggerated, 

 and extremely incorrect and delusive. I do not mean to assert, and can- 

 not be expected to prove, the negative of the assertion of such abundance 

 of green sand. But, from all my means for arriving at conclusions, it is 

 my confident belief that but few of the bodies of miocene marls in Vir- 

 ginia contain as much as 2 per cent, of green-sand — if even as much 

 as 1 per cent. ; and that an average proportion, throughout any con- 

 siderable digging for manure, of as much as 5 per cent, of green- 

 sand is extremely rare. The largest proportion (estimated by the 

 eye) that I ever found was supposed to be 5 per cent. ; and that was in a 

 very peculiar marl, found at Coggins Point farm and elsewhere in that 

 neighborhood, or rather a loose calcareous sand, which forms the over-lying 

 layer of compact blue marl. This sand contains only about 20 per cent, 

 of finely divided shelly matter, and the whole mass would appear, to slight ob- 

 servation, similar to and as poor and as loose as the deep sands of the roads 

 through a sandy country. But few persons would have used this sand for 

 manure — or would have dignified it by the name of marl. However, the 

 ease with which it could be worked, and the necessity for removing it to 

 uncover the better marl below, induced me to carry out and apply it as a 

 second dressing to an adjacent part of a field which had been just before 

 marled. The efiects were so marked, and so superior to the single marling, 

 that I was ready to believe that the green-sand caused the difference. 

 The loose calcareous sand mentioned at page 201, which one of my neigh- 



