1839] 



Trap Dykes in the Sienite of Ambooi\ 



295 



first to show that neither fluidity, nor viscidity, are necessary for crystal- 

 lizalion, I proceed to the consideration of certain facts included in class — ■ 



(5). In the collection of a friend, I had an opportunity of examining 

 * fragment of sandstone, which had originally formed part of the floor of 

 ■a baker's oven. On breaking up the floor for the purpose of repairing 

 it, the whole of the lower portion of the sandstone was found most 

 i-egularly, and beautifully crystallized, in prismatic columns of 6 or 8 

 sides, being the very forms so frequently assumed by basalt, and 

 certain other rocks of igneous origin, and exhibited, on a gigantic 

 scale, at the Isle of StafFa and the Giant's Causeway. The sandstone 

 •was I think about 2 or 2i inches thick, while the columns extended 

 from a thin layer at the upper surfiice, of about i- of an inch in thick- 

 ness, down throughout the remaining thickness of the mass. Look- 

 ing at the exposed surface which formed the floor of the oven, no 

 signs of the column beneath could be detected, and only when a frac- 

 ture was made were they discovered. The sandstone was taken from a 

 quarry, the rock of which was a member of the coal series ; its texture 

 was close, and granular, and its general appearance proved, that though 

 the heat to which it had been subjected, was suthcient to produce 

 erystailization, it had not in the slightest degree, caused it to fuse. 

 In farther illustration of this point, it may be stated, that Professor 

 Mitseherlich found, on exposing j)rismatic crystals of sulphate of 

 jiickel,* in a close vessel, to no stronger heat than that of the sun, 

 that, though externally unchanged, yet, on being broken up, were whol- 

 ly composed of octahedrons ; while the same cause, changed, in a few 

 iseconils, prismatic crystals of zinc, also, into octahedrons. Crystals 

 of sulphate of magnesia and of sulphate of zinc when boiled in alcohol 

 gradually lose their transparency, and on being opened are found to 

 be co?nposed, internally, of numberless minute crystals, totally different 

 in form from the originals. Most striking, indeed, are the views such 

 facts give us of the state of the matter by which we are surrounded? 

 all seems in relative motion, and substances w'hich to our senses seem 

 as hard as adamant may, and indeed, judging from the preceding- 

 facts, actually are in a state of continued and increasing motion — who 

 can say, but that the interior even of the diamond, excited by no greater 

 cause than the warmth of the hand that wears it, would, were its particles 

 and the efl'ects produced upon them equally appreciable by our senses, ex'" 

 hibit a scene of as much turmoil, and change, as that produced by a 



* Mrs. Soraerville's Connection of the Science!?. 



