CALCAREOUS MANURES— APPENDIX. 233 



bors supposed (from its good effects) to be rich in calcareous earth, is pre- 

 cisely like mine in general appearance, and in position in the bed ; and 

 appears to have a like unusually large proportion of green-sand, which no 

 doubt served to produce part of the benefit which was ascribed wholly to the 

 carbonate of lime. This peculiar deposite furnishes the only cases known to 

 me of a miocene marl being rich enough in green-sand for the benefit from 

 the latter to be known. And even this benefit would not have been distin- 

 guished or suspected, but that the poverty of the earth in calcareous matter 

 required it to be applied very heavily. The much thicker body of compact 

 marl, lying under this poor calcareous sand, contains (by supposition) not 

 so much as 2 per cent, of green-sand. 



But it is true, that when attention was not particularly directed to green- 

 sand, proportions not exceeding 5 or 6 per cent, might have escaped the notice 

 of one who had handled and examined the specimens of marl, or who even 

 analyzed them, merely with a view to their proportions of calcareous matter. 

 But proportions so large as 40, 30, or even 20 per cent, of green-sand could 

 not thus escape even careless and superficial observation; for even the 

 smallest of these proportions would give a very manifest greenish or gray 

 tint to any otherwise light-colored marl. Knowing the great uncertainty 

 of the guessings at proportions of green-sand naturally intermixed with marl 

 or other earth, I did not rely on them except as to the absence of any very 

 large proportion. For more accurate testing, the clayey parts were washed 

 off in water ; in others the calcareous parts were also removed by weak 

 acid. And for still better means of judging by comparison, I mixed toge- 

 ther, in different known proportions, measured quantities of light-colored 

 marl (such as arc all those about Williamsburg,) and pure green -sand pre- 

 pared by washing some obtained from the richest beds in New Jersey. And 

 of such artificial compounds, examined by the eye both when dry and in 

 powder, and wet, and also after being again dried in mass, the admixture of 

 green-sand, even when as small as 10 per cent, was obviously more abun- 

 dant than in the miocene marls reputed to be among the richest in green- 

 sand. Under these circumstances, without denying the possible existence 

 of such cases, it is proper to wait for and to require further proof of such 

 large proportions as 20 to 40 per cent. 



But there is much better support for my position, of the general scarcity 

 of green-sand in miocene marls, than any proofs, positive or negative, that 

 I can adduce, presented by Prof Rogers himself in his ' Report of the pro- 

 gress of the Geological Survey' for 1837. He therein gives a tabular state- 

 ment of 148 specimens selected by his assistants, and their analyses made 

 under his own direction. It is to be presumed that so many specimens, and 

 thus obtained, must present a fair and correct average of general quality of 

 the marls of the region in which they were found ; or at least that their con- 

 tents would not be too little favorable to the geologist's preconceived opinions. 

 The specimens were from 18 counties, viz. : Lancaster, Westmoreland, Rich- 

 mond, Northumberland, King George, Mathews, Middlesex, Gloucester, 

 King and Q,ueen, King William, Essex, Isle of Wight, Nanseraond, Elizabeth 

 City, Surry, Prince George, James City, and Warwick. Of these 148 speci- 

 mens, of one only (S. Downing's, Lancaster,) is the quantity or proportion 

 of green-sand stated with any approach to precision. This is said to contain 

 " 10 or 12 per cent, of green-sand," and only 17 per cent, of carbonate of 

 lime. Of five others, the green-sand would seem to be in notable quantities, 

 but as no numbers or proportions are named, it may be inferred that the 

 proportions were deemed less than the one just stated. These five are 

 described as follows, in regard to this ingredient : Callahan's, Lancaster, 

 "large grains of green-sand in considerable quantity;" Gloucester Town, 

 " richly specked with green-sand ;" Saunders', Isle of Wight, (one only of 



