GYPSEOUS EARTH OP JAMES RIVER. 455 



cessary to treat in advance and separately of the peculiar earthy 

 compound, called " green-sand" by geological writers, of which the 

 large admixture, and sometimes even larger proportion, or other- 

 wise some other ingredient usually accompanying the green-sand, 

 gives additional value and peculiar character and action to the greater 

 number and quantity of the eocene marls yet known in Virginia. 

 But important and valuable as may be the green-sand in itself, and 

 necessary to be considered in connexion with the subject of eocene 

 marl, with which it is so inseparably connected, I wish especially to 

 avoid confounding the two earths under one name or one character j 

 and to be understood as protesting against the prevalent error, in 

 giving currency to which scientific writers have concurred with the 

 unlearned cultivators, of applying to the non-calcareoits green-sand 

 earth the name of " marl," and thus adding another, and the most 

 important, to the many previous misapplications of this wonderfully 

 misused and misunderstood term. This misapplication is universal 

 in New Jersey, where the green-sand earth is most abundant, and 

 is generally very rich in its distinguishing ingredient (usually con- 

 taining 75 to 90 per cent, of pure green-sand), and where this earth 

 has been long and is now extensively used as a manure, and has 

 been found to be of great value as a fertilizer. I shall hereafter 

 refer to both the points of resemblance and of difference (both of 

 which are important and interesting,) between this green earth of 

 New Jersey and that of James river ; but, for the present, my re- 

 marks will be confined to the latter, and its use as manure, as 

 known principally, and indeed almost entirely, from my own ob- 

 servations and practical experience, there having as yet been but 

 few trials of it made by other persons. 



It was mentioned in the foregoing section, that the first notice or 

 observation of the eocene marl, on James river, was induced by the 

 previous discovery and examination of the green or gypseous earth 

 the latter being the universal underlying bed of the former, and 

 connected with it in more respects than merely its subjacent posi- 

 tion. It was my chance, or the result of habits of observation of 

 marls and other earths, and not of any scientific knowledge or pre- 

 vious preparation for such investigations, which led me, in 1817, to 

 be the first to observe this bed of green earth in the river banks of 

 Evergreen and Coggins Point, and to trace it where visible along 

 the intermediate ground, a distance of about eight miles. Since 

 then, it is known to be much more extended ; for it not only under- 

 lies all the eocene marl of the same neighbourhood, wherever that is 

 found, and part of the yellow sandy miocene, but also extends be- 

 yond, and is found at various places where no eocene or even mio- 

 cene marl is present. The most western limit, seen after a long in- 

 terval, or concealed existence of this formation, is at Petersburg, 

 where it shows in the ravines south of Poplar Lawn, 



