CALCAREOUS MANURES— PRACTICE 93 



along the river bank, this bed lies on another earth, of peculiar cimracter 

 and appearance, and which, in many places, exhibits gypsum in crystals of 

 various sizes. This earth has evidently once been a bed cf fossil shells, 

 like what still remains above ; but nothing now is left of the shells, except 

 numerous impressions of their forms. Not the smallest proportion of cal- 

 careous earth can be found, and the gypsum into which it must have been 

 changed (by meeting with sulphuric acid, or sulphuret of iron,) has also 

 disappeared in most places ; and in others, it remains only in small quantities 

 — say from the smallest perceptible proportion, to fifteen or twenty per 

 cent, of the mixed mass. In some rare cases, this gypseous earth is suffi- 

 ciently abundant to be used profitably as manure, as has been done, by 

 Mr. Thomas Cocke, of Tarbay, as well as myself It is found in the great- 

 est quantity, and also the richest in gypsum, at Evergreen, two miles be- 

 low City Point. There the gypsum frequently forms large crystals of va- 

 ried and beautiful forms. The distance that this bed of gypseous earth 

 extends is about seven miles, interrupted only by some bodies of lower 

 land, apparently of a more recent formation by alluvion. 



In the bed of gypseous marl above described, there are. regular layers of 

 a calcareous rock, which was too hard to use profitably for manure, and 

 which caused the greatest impediment to obtaining the softer part. This 

 rock contains between eighty-five and ninety per cent, of pure calcareous 

 earth, besides a little gypsum and iron. It makes excellent lime for cement, 

 mixed with twice its bulk of sand, and has been used for part of the brick- 

 work, and all the plastering of my present dwelling house, and for several 

 of my neighbors' houses. The whole body of marl also contains a minute 

 proportion of some soluble salts, which possibly may have some influence 

 on the operation of the substance, as manure or cement. 



Thus, from the examination of a single body of marl, there have been 

 obtained not only a rich calcareous manure, but also gypsum, and a valu- 

 able cement. Similar formations may perhaps be abundant elsewhere, and 

 their value unsuspected, and likely to remain useless. This particular body 

 of marl has no outward appearance of possessing even its calcareous cha- 

 racter. It would be considered, on slight inspection, as a mass of gritty 

 clay, of no worth whatever. 



The last preceding paragraphs present, as in the previous editions, my 

 earliest views of this particular bed of marl. Further information has 

 taught that it is of the eocene, or more ancient formation ; and that the un- 

 derlying stratum, (which is usually not at all calcareous.) which I formerly 

 named and treated of as " gypseous earth," is what geologists call " green- 

 sand," a term still less descriptive, and not at all more accurate. A full 

 account of both of these bodies will be given in the Appendix. 



This gypseous marl has been used only on sixty acres, most of which 

 was neutral soil, and generally, if not universally, with early as well as 

 permanent benefits. The following experiments show results more striking 

 than have been usually obtained; but all agree in their general character. 



Experiment \S. 



1819. Across the shelly island numbered 3 in the examinations of soils, 

 (page 38,) but where the land was less calcareous, a strip of three quarters 

 of an acre was covered with muscle-sliell marl, a deposite on parts of the 

 river banks supposed to have been made by the aboriginal inhabitants. 

 Touching this, through its whole length, another strip v/as covered with 

 gypseous marl, 53 per cent., at the rate of 250 bushels. 



Results. 1819. In corn. No perceptible effect fiom tlie muscle shells. 

 The gypseous marling considerably better than on either side of it. 



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