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A R E N Æ.

Sect. IV. Tlie Brown SANDS.

A. Such as are pure and free from heterogene particles.

i. Arena fusca , tenuissma 5 hebes.

Fine j brown Sand.

This is a fine but disagreeably colour’d Sand, generally found at considerable depthsand in but thin strata. It is remarkably fine and small, not very heavy; of a dull,uniform, pale brown, with scarce any brightness; and not easily distinguishable ata distance from an heap of dust; its particles are pretty uniform and regular in size,it feels considerably harsli and sharp between the fingers, and Look up in water fettlesbut slowly, and leaves a muddiness in it.

Examin’d by the Microscope, it appears compos’d of particles much of the famesize and shape, resembling small Pebbles, of unequal surfaces, moderately transparent,but not very bright and all stain’d with a very faint brown.

It makes no effervescence with Aqua Fortis.

It burns to a pale reddish brown.

It is frequent in the Sand pits about Woolwich and Blackheath, under the strataof the more common Sands.

This is one of those species of Sand of so little splendor, or crystalline brightness, asto give some suspicion of its not being a genuine body of this Class; but this is evinc’d be-yond contradiction or doubt, by its refusing to ferment with acids, a ready and an unerringtest for these bodies, and one that before the species of this Class were arrang’d into theorder I have here plac’d them in; I made each of them severally undergo in companywith the ingenious and learned Dr. Parsons, one of the few of the present age who are forestablishing natural history on its true principles, and judging of the subjects of it, notfrom the uncertain accounts of others, but from nature itself; and whose disquisitionson. the Rhinoceros, and some other subjects of the animal world, will do him honour,when the labours of many who now triumph in the republick of letters shall have beenlong forgotten.

2. Arena crajjijjima , splendida , p alii de fusca.

Coarse , shining , pale browfi Sand.

This is a bright and elegant Sand, generally lying deep and in thick strata; it is oneof the largest and coarsest Sands I know, not remarkably heavy, of a very pale brown,and considerably bright and sparkling ; its particles are very uniform and regular insize : It feels very coarse and hard, but not so sharp as many others between the fingers,and shook up in water, settles immediately, without leaving the least foulness.

Examin’d by the Microscope, it appears an assemblage of particles much of the fameshape and size, they are all somewhat roundish, moderately bright and transparent, andting’d in different degrees with a very pretty pale brown.

It makes no effervescence with Aqua Fortis.

It burns to a pale brownish red.

It is common in the Sand pits about Woolwich, and often found on the Lores of theThames, and other rivers.

3. Arena crassissma , splendida , fusco purpurea.

Coarse , purplish brown , shining Sand.

This, when strictly examin’d, is one of the most singular and remarkable bodiesof this Class. It is very large and coarse, of great weight, and of a deep duskypurplish brown or chocolate colour, interspers’d with white; it has a great deal ofbrightness, but that is wholly owing to the white particles, for the brown are all dulland dead, its constituent particles are all much of the fame size and figure; it feelsvery rough and sharp between the fingers, and Look up in water subsides very quick-ly, leaving a slight yellowish muddiness in it.

Examin’d by the Microscope, it makes a most singular and pleasing appearance;its particles are much of the fame size, and all of one shape, approaching to round-ness, and resembling ordinary Pebbles; they are of two very different colours, whiteand brown or chocolate colour ; the former always of smooth, the latter of veryrough and irregular surfaces; a close examination, however, shews these brown

particles