CALCAREOUS JVIANURES— APPENDIX. 



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north of City Pt)int. This marl 1 recognized to be the same, by a specimen 

 recently brought me for examination. It is below the surface of swampy 

 ground, and is colored dark gray. It is much fuller of green-sand, and 

 indeed in that respect makes some approach to the green-sand marls of the 

 Pamunkey, of which the nearest exposure is only 16 miiles from this place. 

 It is probable that the marl extends continuously from the one place to the 

 other, and may be found throughout the interval by deep digging. 



(e) THE GYPSEOUS EARTH OR GREEN EARTH OF JAMES RIVER. 



Before proceeding to consider the next and only remaining known 

 variety of our marls, the eocene green-sand marl, it is necessary 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, gives additional value and peculiar character and 

 action to the greater number and quantity of the eocene marls yet known. 

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

 sary 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; 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-calcareous green-sand earth the name of "marl," and thus adding ano- 

 ther, and the most important one, to the previous misapplications of this 

 wonderfully misused and misunderstood term. This misapplication is uni- 

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

 generally very rich in its distinguishing ingredient, (usually containing 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 re- 

 semblance and of difference (both of which are impoi'tant and interesting) 

 between this green earth of New Jersey and that of James river; but, for 

 the present, my I'emarks will be confined to the latter", and its use as ma- 

 nure, as known principahy, and indeed almost entirely, from my own 

 observations 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 obser- 

 vation 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 position. It was my chance, or 

 the result of habits of observation of marls and other earths, and not of 

 any scientific knowledge or previous preparation f^r such investigations, 

 which led me, in 1817, to be the first to observe this bed of green earth in 

 the river banks of Ever-green 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 neighbor-hood, wherever that is found, 

 and part of the yellow sandy miocene, but also extends beyond, and is 

 found at various places where no eocene or even miocene marl is found. 

 The most western limit, seen after a long interval or concealed existence 

 of this formation, is at Petersburg, where it shows in the ravines south of 

 Poplar Lawn. 



What fir-st directed my attention to this earth was the existence in the 



