144 GYPSEOUS MARL OF COGGINS POINT. 



the experiments. Some of these applications will be described, 

 that other persons may draw their own conclusions from them. 



The cause of these manures being applied in conjunction was 

 this. A singular bed of marl lying under Coggins Point, and the 

 only one within a convenient distance to most of the neutral soil 

 of that farm, contains a very small proportion (perhaps about one 

 per cent.) of gypsum, scattered irregularly through the mass, 

 seldom visible, though sometimes and very rarely to be met with 

 in small crystals. The calcareous ingredient, on a general average 

 carefully made, was found to be 62 per cent. If this manure had 

 been used before its gypseous quality was discovered, all its effects 

 would have been ascribed to calcareous earth alone, and the mosfc 

 erroneous opinions might thence have been formed of its mode of 

 operation. 



What led me to suspect the presence of gypsum, in this bed of 

 fossil shells, was the circumstance that throughout its whole extent, 

 of near a mile along the river bank, this bed lies on another earth, 

 of peculiar character and appearance, and which, in many places, 

 exhibits gypsum in crystals of various sizes. This earth has evi- 

 dently once been a bed of fossil shells, like that which still remains 

 above ; but nothing now is left of the shells, except numerous im- 

 pressions of their forms. Not the smallest proportion of calcare- 

 ous 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 propor- 

 tion, to fifteen or twenty per cent, of the mixed mass. In some 

 rare cases, this gypseous earth is sufficiently 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 greatest quantity, 

 and also the richest in gypsum, at Evergreen, two miles below City 

 Point. There the gypsum frequently forms large crystals of varied 

 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 (at Shellbanks), and 

 for several of my neighbours' houses. The whole body of marl 

 also -con tains a minute proportion of some soluble salts, which pos- 



