488 PROFESSOR ROGERS' DISCOVER y. 



ture to be general as to other miocene marls ; and that the propor- 

 tions of green-sand so contained were large enough to form useful 

 additions to, and in some cases the most valuable portion of the 

 manuring ingredients of such marls (Farmers' Register, vol. ii., p. 

 129). At a later time, he added to like general opinions and state- 

 ments the following : " In some of these deposits [marl beds in the 

 vicinity of Williamsburg], so large a proportion as 80 and in 

 some specimens 40 per cent, [of pure green-sand] has been found ; 

 and in cuses like this, if we are to trust to the experience of New 

 Jersey, a very marked addition to the fertilizing power of marl 

 must be ascribed to the presence of this ingredient." (Farmers' 

 Register, vol. ii., p. 747.) In a subsequent communication to the 

 Philosophical Society of Philadelphia in 1835, and again in the first 

 report of the geological survey of Virginia, the material parts of the 

 above statements 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 diffu- 

 sion 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 [1842], many proprie- 

 tors consider that their marls are peculiarly valuable because of the 

 supposed large proportions of green-sand therein ; such opinions 

 being founded either on the publications, or, with still more confi- 

 dence, upon the personal examinations and verbally expressed 

 opinions of the former state geologist. 



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

 specimens of other beds, have been very extensive ; and my atten- 

 tion 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 Professor Rogers had pronounced to be jyery 

 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 Professor 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 quan- 



