226 CALCAREOUS MANURES-APPENDIX. 



of the bed of marl show an average width of three or more miles. 

 Throughout this area, it is found in great abundance at numerous points — 

 though of great variety of appearance and of value at different elevations, 

 and in very different degrees of accessibleness, or ease of working. 



This marl every where has its calcareous portion (which is usually small 

 in comparison to good miocene marls,) intermixed with a large proportion 

 of green-sand. The calcareous earth varies from 10 to 40 per cent, at 

 different diggings, or different layers at the same locality; and the green- 

 sand perhaps from 20 to 40 per cent, as estimated by the eye.* In some 

 j)laces, the one ingredient predominates in quantit}'', and elsewhere the other. 

 No one specimen has been found rich in both of these ingredients. So far 

 as known, the remainder of the whole mass, (as in miocene marls,) is of 

 silicious sand and day. 



Below this green-sand marl lies a bed of brownish green earth, slightly 

 sprinkled with small eocene shells and their fragments, but which, or all the 

 calcareous matter present, would very rarely amount to 5 per cent., and 

 sometimes not 2 per cent. To this lower stratum is also applied the term 

 marl by the proprietors, as is done in New Jersey. But this term should 

 not be given where the calcareous earth is so small in amount as 5 per 

 cent. Though it may be impossible to draw a precise line of demarkation, 

 either on the banks, or to di.stinguish them by definition in words, still these 

 two earths ought to be known by different terms. By green-sa7id earth or 

 green earth, will be here understood the lower stratum, or any other having 

 green-sand in considerable quantity, and not more than 5 per cent, of cal- 

 careous earth, if any. And I would not consider any as green-sand marl, 

 that did not have as much as 10 per cent, of carbonate of lime— leaving as 

 doubtful and debatable, such as had more than 5 and less than 10 per cent. 



The Pamunkey river is very narrow and yet deep, and its high banks, 

 or cliffs, formed generally of green-sand marl and green-sand earth, are 

 nearly perpendicular. The remarkable power which green-sand has of 

 resisting the v/ashing of water, is doubtless the cause of the narrowness 

 of this river, and of the forces of its strong ordinary tides and violent current 

 in freshes having operated to deepen the channel, instead of wearing away 

 the banks. Slides of the banks,"or land-slips, are frequent ; large masses 

 of the upper stratum of soil breaking loose, and, with the growth of large 

 trees, slip down the steep bank into the river, scraping clean the exposed 

 parts of the strata in the descent. In this waj', sections of the bank 40 feet 

 or more in height are exposed more completely to view than would be 

 done by the progress of any diggings for marl, however rapid or extensive. 



The general appearance of any one of such sections, taken at one of 

 the several exposures from one to five miles below Newcastle ferry, is as 

 follows: At top, below the soil and ordinary sub-soil, (or diluvial earth,) of 

 say 10 to 20 feet, there is generally, though not ahvays, a stratum of some 

 4 or 5 feet of olive colored earth, so called, and which term is descriptive 

 of the appearance. This earth is of a greenish brown color, contains 

 small shark.s' teeth and fishes' bones, but no shells. Its appearance so nearly 

 resembles the marl below, that it has been sometimes dug and used instead, 

 either from the ignorance of the conductor or the carelessness of the la- 

 borers. It is entirely worthless as manure, as has been proved by careful 

 experiments. A well dug (to obtain water) at Piping Tree ferry, pene- 

 trated very deep into this olive earth without reaching marl. The earth 

 thus removed was used as manure, without any benefit being produced. 



* These and all others named supposed proportions of green-sand were written before 

 receiving Professor Shepard's report. His analyses make it seem probable that all my 

 guesses of such proportions were too high. 



