VOL. XXin.] PHILOSOPHICAL TRANSACTIONS. 645 



inclose substances of a very different nature from themselves ; as appears by the 

 shells in Sussex marble; and the stones found in our coal-pits, and known 

 among the workmen by the name of cat-heads : these are found in a particular 

 stratum near the coal, and inclose a fern, or sometimes a polypody leaf in the 

 middle ; and for that reason being struck with a hammer, they very readily 

 break there : they seem to be a sort of ironstone, akin to that which they call 

 in Staffordshire ballmine, and Dr. Lister, minera ferri pilaeformis. And to give 

 an instance that one and the same piece of rock does not always shoot into 

 stone at one and the same time, but first one part of it and then another, 

 and that not after the same regular manner, I have a piece of rock crystal, 

 •where may easily be observed the modus concrescendi in the middle, different 

 from that of the outside ; nay, sometimes I have seen in the middle of some 

 transparent stones, a small drop that never would take the solid form of the 

 rest of the stone at all. 



The 3d curiosity was also sent me from the same very kind friend Dr. Cay ; 

 it is a piece of an iron-bolt, 1 inches long, found in a stone quarry, now re- 

 turned into iron ore again ; this being a property that iron has, and no other 

 metal, as Dr. Lister observes in his Journey to Paris. 



4thly, The copper ore so regulated shot into an octoedrous form, was sent 

 me from Sweden by Mr. William Sykes of Stockholm, merchant : it has 8 

 solid triangles, and consequently 6 angular points, and is nearly of the size 

 and figure of the draught of it, fig. 13, pi. 15. It was received from the 

 copper groves at Fahlun, where many more of the same form were then 

 found. 



Extracts of tivo Letters ft om the Rev. Abraham de la Pryme, F. R, S. concern- 

 ing the Subterraneous Trees at Hatfield Chace, the Bitings of Mad Dogs, &c. 

 N° 277, p. 1073. 



Being at Hatfield lately, I was told by several gentlemen, that about 20 years 

 before, died one Saunderson of that town, aged near SO; whose father, much 

 of the same age, frequently assured him and others, that he could very well 

 remember many hundreds of large fir-trees that grew in those levels, standing 

 here and there, in a decaying condition, whose tops were all dead, yet their 

 boughs and branches always green and flourishing : and John Hatfield, Esq. 

 who is not above 40 years of age, has by him a large twig that his father 

 plucked off from a green and flourishing sprout of fir, that grew from 

 the great root of one of the same kind in the*e commons. And an old 

 man of Croul has heard his father say, that he coul<l remember multitudes of 

 shrubs and small fir-trees growing here before the drainage, while this country 



