604 Transactions of the American Institute. 



the spade down into it, requires a vigorous and steady push, and 

 reminds one of pressing a thin-bladed knife into a new-made 

 cheese. It comes up in chunks or cakes, retaining, for some 

 time, the shape of the spade that cut its way, foot by foot, into the 

 deposit. But a few weeks exposure reduces the pile to a grayish 

 green color, friable, crushing between the fingers, and showing a tine 

 olive reen, sand-like substance. Rub a pinch of it for a short time 

 in tlie palm, till warmth and friction have driven off most of the 

 moisture, and you have a light green powder and a dark green col- 

 lection of roundish grains, not sand, not clay, having no angular or 

 fractured edges or points. These we call the gunpowder grains, and 

 they are the peculiar thing in Jersey marl. ' Let us scrutinize them. 

 First, after rubbing them dry, as I have described, lay > them on 

 smooth paper, and apply a clear glass that will make this sand, as it 

 appears to thi unassisted eye, look as large as onion seed, the largest 

 of them not smaller than small peas. What do we see in such a 

 field? It Is no longer sand, but a group of rounded forms, not 

 spherical, but with lobes or swellings, like those on an irregularly 

 grown tomato ; between these lobes are little furrows filled with a 

 fine pale green powder. The grains are of a dark olive-green hue, 

 and the crust that walls in these grains is quite firm. But press upon 

 one of them with a pin head or the tip of a knife blade, and it 

 breaks down with a brittle crash and falls into irregular fragments of 

 a pale-greeii color. Put these fragments under a higher power, and 

 the microscope gives us only negative testimony. The molecule of 

 green sand crushed gives no regular form, no suggestion of a cube, 

 or a prism, or a pyramid ; no convolution or whorl, as though it 

 might be the fragment of a minute shell ; nothing of all this, but 

 simply .an irregular particle, which by slight pressure falls into 

 smaller but still shapeless atoms. There is no hint or vistage of 

 either a crystalline or an organic law under which it was formed. 



Suppose now, having found out all that the eye alone or aided by 

 lenses, can testify, we set up a nicer scrutiny, and call in the aid of 

 alembics, retorts, and reagents. What will chemistry reveal ? New 

 Jersey marl, or green sand, has been analyzed many times in different 

 laboratories of the country and in Europe, with results that closely 

 correspond. All the analysts find potash, all find phosphoric acid, 

 all find lime generally, as a carbonate, and abstracting these sub- 

 stances that have fertilizing value, the bulk of green sand is made up 

 of clay, sand, and iron. 



