180 PHILOSOPHICAL TRANSACTIONS. [aNNO 1675. 



over with a white farinaceous matter, that is, with these fibres calcined by the 

 rays of the sun and warm air beating upon them. Of what figure these fibres- 

 Were, whether round or angular, I could not well discern. But I take these 

 fibrous and thread-like shootings of alum and vitriol to be most genuine and 

 natural ; and their angular shootings, after solution, into cubes and rhomboides, 

 to be forced and accidental; salts of very different natures, as well vegetable as 

 fossil, by a like process in crystallizing of them, being observed to shoot into 

 like figures. But this is not my purpose at this time. 



II. Of an Odd Figured Iris. See Jig. 3 and 4, pi. 7. 



I have not observed any rock or sort of stone, whether metalline or more 

 common, which has not its different sort of spar, shot in some part or other of 

 its bed or seams. And these spars differ not only in their colours and other 

 accidents, but eminently too in their figure. To pass by divers which I have 

 collected, I shall describe one of a very curious figure, and which, though very 

 common in our blue lime-stone rocks, out of which plenty of lead ore is gotten, 

 yet is not, that I know of, mentioned by any author. These crystals are mostly 

 of a black water, like the black flint in chalk-hills; but there are of them, which 

 have a purplish or amethystine colour; and some there are as clear as crystal. 

 They adhere to the seams of the rock, whether between bed and bed, or where- 

 ever there are cross and oblique veins through the very substance of the bed. 

 The smaller the veins the less the Iris. Some are as small as wheat corns, and 

 others a hundred times larger. They shoot from both sides of the seam, and 

 mutually receive one another. They are figured thus, viz. a column of six 

 planes very unequal as to breadth ; the end adhering to the rock is always rug- 

 ged, as a thing broken off; the other end of the column consists of three quin- 

 angular planes, very little raised in the middle: these planes too are very unequal. 

 However they may be straightened and compressed in their shooting, yet the num- 

 ber of planes mentioned both of the column and top is most certain. The places 

 where infinite of them may be had, are llainsborough Scar on the Kibble; also in 

 a stone- quarry near Eshton Tarne, in Craven. 



III. Glossopetra tricuspis non-serrata. Fig. 1 and 2. 



Mr. Ray, in his travels, has these words concerning the Glossopetrae, p. 115. 

 " Of the Glossopetrae, I have not yet heard that there have been any. found in 

 England ; which I do not a little wonder at, there being sharks frequently taken 

 upon our coasts." I have had out of the isle of Sheppey, in the river of Thames, 

 very sharks teeth dug up there ; which could not be said to be petrified ; though 



