RICHEST MIOCENE MAULS. 443 



quest, and for niy examination, an average portion taken was com- 

 posed as follows : 



1780 grains, separated mechanically, by the sieve and by washing 

 and subsidence in water, consisted of 



Carbonate Fine argillaceous Silicious Green-sand. 



of lime. jarth. sand. 



1036 grains of shells and coarse 

 fragments, nearly pure, and 

 so counted, - - 1036 



483 grains of fine shelly frag- 

 ments, &c., which consisted 



of 268 - - - 120 45 



277 grains fine yellow clay, &c., 



which consisted of - 65 212 



34 loss in the process. 



1780 1369 212 120 45 



Which may be stated of parts to the hundred, thus : 



100 grains of marl contained of carbonate of lime, - 77 grains. 



Silicious or quartz sand, very pure and white, - - 6| " 



Green-sand, _____>__ 2|" 



Fine yellow clay or argillaceous earth (and the loss in 



the latter process), ....._ 13| 



100 



The richest bodies of these marls show very few shells, or even 

 fragments, and have a homogeneous texture and appearance to the 

 eye, like a very impure chalk or sandy clay. Such marls are 

 found in James City, New Kent, King "William, and Middlesex 

 counties. The following are some of them of which I have analyzed 

 specimens : - 



FROM 

 King William, (Lipscomb's land) 82 pr. ct. of carbonate of lime. 



" (Slaughter's land) 88 " 



New Kent, (Mount Prospect) 88 " " " 



Middlesex, (Oaks' land) 83 " " " 



Most of these marls are soft enough to be used for manure as 

 dug from the pits ; but the hardest lumps may need burning to 

 lime. Any marl hard enough to need burning, and as rich 

 as 85 per cent., will make good lime for cement, as well as for 

 manure. 



Under a peculiar combination of circumstances, the great rich- 

 ness of some marls operates to lessen the value of the body as ma- 

 nure. Rain-water, when just fallen, always contains come carbonio 

 acid, which admixture causes it to be a solvent of carbonate of lime. 

 When rain-water then can descend by percolation into rich dry 

 marl ; in its passage it dissolves some of the calcareous matter, 



