ὀστεοκόλλα, in Natural History, a white or ash-coloured, fparry substance, in shape like a bone, and by some supposed to have the quality of uniting broken bones, on which account it is ordered in fome plasters; a fuppofition, we fear, which is not warranted by experience. It is found in long, thick, and irregularly cylindric pieces, which are in general hollow, but are sometimes filled up with a marly earth, and sometimes contain within them the remains of a stick, round which the osteocolla had been formed; but though it is plain from thence that many pieces of osteocolla have been formed by incrustations round sticks, yet the greater number are not fo, but are irregularly tubular, and appear to be formed of a flat cake, rolled up in a cylindric fhape. The crusts of which these are composed do not form regular concentric circles round the internal cavity, as might have been the case had they been formed by incrudation. On the other hand, they plainly show that they were once fo many thin strata, composing a flat furface, which has afterwards been rolled up, as one might do a paper three or four times doubled, into two, three, or more spiral lines; in which cafe, each fingle edge of the paper would be everywhere a regular point of a continued spiral line drawn from a given point; but they would by no means be fo many detached concentric circles. The osteocolla is found of different fizes, from that of a crow-quill to the thickness of a man's arm. It is composed of fand and earth, which may be separated by wafhing the powdered osteocolla with water, and is found both in digging and in feveral brooks, in many parts of Germany, and elsewhere. It is called hammoefius in many parts of Germany. It has this name in thefe places from its always growing in fand, never in clay, or any folid foil, nor even in gravel. Where a piece of it any where appears on the furface, they dig down for it, and find the osteocolla branches run ten or twelve feet deep. They ufually run straight down, but fometimes they are found spreading into many parts near the furface, as if it were a subterraneous tree, whose main ftem began at 12 feet depth, and thence grew up in a branched manner till met by the open air. The main trunk is ufually as thick as a man's leg, and the branches that grow out from it are thicker near the trunk, and thinner as they separate from it. The thinnest are about the fize of a man's finger. The people employed to collect it, when they cannot find any mark of it on the furface, fearch after the fpecks of white or little lumps of whitish foft matter, which they find lying in various parts on the top of the fand. Thefe always lead them either to a bed of perfect osteocolla, or to fome in the formation. If they miss of it, they fill find a fubfance like rotten wood; which, when traced in its courfe, is found to proceed from a main trunk, at the depth of that of the osteocolla, and to spread itfelf into branches in the fame manner. The diggers call this fubfance the flower of osteocolla, or hammoefius.

The osteocolla found in the earth is at firft foft and ductile, but in half an hour's time, if expofed to the air, it becomes as hard as we find it in the fhoes. The method to take up a perfect piece for a fpecimen is to open the ground, clear away the fand, and leave it fo for an hour or thereabouts: in this time it will harden, and may be taken out whole. It is certain, that the osteocolla is produced at this time; for if a pit be cleared of it, there will more grow there in a year or two, only it will be fofter, and will not harden fo eafily in the air as the other. What the rotten fubfance refebling the decayed branches of trees is, we cannot determine, unlefs it really be fuch; but the opinion of the common people, that it is the root of something, is abfurd, becaufe its thickest part always lies at the greatest depth, and the branches all run upwards. The osteocolla is a marly fpar, which concretes round this matter; but what it is that determines it to concrete no where on the fame ground but about thefe branches, it is difficult to fay. The rottennefs of this fubfance, which forms the basis of the osteocolla, renders it very liable to moulder and fall away; and hence it is that we ufually fee the osteocolla hollow. Sometimes it is found folid; but in this cafe there will be found to have been a vegetable matter ferving as its basis, and inftead of one branch, it will be found in this cafe to have concreted about a number of fibres, the remains of which will be found in it on a clofe examination. See Phil. Tranf. No 39.