VOL. XXXV.] PHILOSOPHICAL TRANSACTIONS. 241 



calcine substances of this kind, which in this tooth was to such a degree, that 

 it was grown extremely brittle, and ready to fall to pieces; and had also acquired 

 an astringent quality common to calcined substances of this kind, which makes 

 them stick pretty close, when held to the tongue. They had altogether the 

 same effect on the very large skeleton, found near Drapani in Sicily, and men- 

 tioned by Boccatius, on that remarkable one found near Tonna, described by 

 Tentzelius ; as also on two teeth found in Northamptonshire, described next 

 below. However it by no means follows from hence, that all teeth and sub- 

 stances of this kind undergo the like calcination by lying long under ground, 

 for there are others, as those found in Iceland, and sent to Thomas Bartholin, 

 which were turned to a perfect hard, flinty substance. 



It serves, in the second place, to ascertain the structure of these teeth, and 

 consequently of ivory in general, to be layer upon layer, or coat upon coat, 

 like the skins in an onion, or rather the annual circles, or rings in trunks of 

 trees. In this piece, belonging to the basis of the tooth, there appeared very 

 visible marks of g coats, some of about -jV of an inch in thickness. Towards 

 the further end of the tooth, where it tapers almost to a point, these several 

 coats also join together into two or three, and those pretty considerably thick. 

 With some care these coats might be further sub-divided into a considerable 

 number of other smaller ones, perhaps no thicker than a common parchment. 

 The very manner of its falling to pieces is an evident proof of its structure, all 

 the fragments being concave within, and convex without, and the lines of con- 

 vexity and concavity, fragments of concentric circles, which the several coats 

 composed, when entire. 



Thomas Bartholin, in his Treatise De Unicornu, observes, that part of a 

 fossil unicorn horn having been calcined by order of Christian the 4th, king of 

 Denmark, it was found to be composed, after the same manner, of thin layers 

 upon layers ; whence he infers, that it was not the horn of an animal, as was 

 commonly pretended, but a tooth, viz. the tooth of a sort of whale in the 

 northern seas, called Narvhal, as he had afterwards an excellent opportunity to 

 verify by one of these unicorn's horns still sticking in the skull of the creature, 

 which was sent to Wormius by Thorlacus Scutonius, bishop of Iceland. Nor 

 is this structure by any means to be considered as an effect of the calcination, 

 whether brought about by the subterranean steams, or by a chemical trial, but 

 is natural to the tooth, as appears in some measure by a piece of ivory, marked 

 1181: but still more plain in another marked 731, where several of these coats 

 are by some disease in the tooth actually separated from each other, like the 

 leaves of a parchment book, the ivory on the other side being still firm and 

 close. This strucure appears likewise from the teeth of the very young ele- 



VOL. VII. I I 



