444 CRYSTALLIZATION OP MARL. 



which is again left solid, and in crystals, by the slow evaporation 

 of the fluid. These crystals of carbonate of lime are slowly added 

 to by every recurrence of the like causes, until the cavities of large 

 shells, and other openings into which the water had settled, are 

 completely filled with crystallization. If layers of marl, less per- 

 vious to water than in general, oppose the descent of the water, the 

 crystallization forms in connected horizontal layers, separated by 

 the thicker layers of softer marl. Such crystallized layers are 

 4>und abundantly in the very rich marl in the cliffs at Yorktown, 

 serving by their stony hardness to impair the otherwise great value 

 of the manure. At Belfield, Col. Robert McCandlish's farm, a few 

 miles higher on York river, the hollows of large shells have been 

 filled with beautiful and brilliant crystals thus formed. In Surry 

 also, on the land of the late William Jones, such crystallization is 

 abundant. For such effect to be produced, there are several con- 

 ditions necessary. The superincumbent earth must be of open 

 texture, and not very thick or rain-water could not pass through. 

 It must not be a hill-side as the water would flow off the surface 

 and not penetrate to the marl. And the marl must be dry or 

 evaporation could not take place, and, of course, crystallization 

 could not. 



Grloucester, though one of the outside marl counties to the east, 

 is most abundantly supplied with marl, accessible on almost every 

 farm, whether of high or of low grounds. It is generally of the 

 poorer yellow kind. But three marked exceptions were seen, 

 which as such deserve to be named. One is the rich clay marl 

 forming the north bank of Ware river on the farm of Mr. Alexan- 

 der Taliaferro. Another is the general sub-soil (as it may be con- 

 sidered from its position) of the lowest land of the farm of Mr. 

 Jefferson Sinclair, near the mouth of Severn river. This is an al- 

 most pure body of coarse shelly powder, or fragments, seldom found 

 larger than two or three grains in weight, and a very few shells, of 

 as minute size, entire enough to be distinguished. This mass of 

 shelly matter is as loose and incohesive as coarse sand, yet is tinged 

 slightly with green by the admixture of greenish clay. A speci- 

 men analyzed contained 72 per cent, of carbonate of lime. (See 

 more full account at page 181, vol. vi. Farmers' Register). The 

 third is the marl used by Capt. P. E. Tabb, and dug from beneath 

 the low grounds on North river. It is a mass of pulverized shells, 

 coloured by red or brown oxide of iron.* 



Blue marl. This is the most common kind in the upper range, 

 or near the western limits of the great marl deposit. Thereabout, 



* This is the marl so abundant, and of easy access, on Toddsbury, the 

 property and residence of the deceased Philip Tabb ; and of which marl the 

 value as manure had not been tried, or suspected, by that experienced and 

 deservedly distinguished farmer, during his long life on that farm. 



