1819.] Greenough on the First Principles of Geology. 457 



graphy and geology, and is not surely entitled to a serious 

 examination or refutation. 



R^ieile and Lametherie were of opinion that rocks exhibiting 

 a foliated, radiated, or fibrous texture have been formed by irre- 

 gular crystallization into groups insulated at their summits, but 

 united at their bases. This opinion is very probable. Our 

 author conceives that in such cases the particles have associated 

 without any regard to polarity ; but I apprehend that this notion 

 is not quite correct. If we suppose the particles of a body to 

 be possessed of poles, we must mean that at one extremity they 

 have the property of repelling each other, while their other 

 extremities have the property of attracting each other. This is 

 what is meant by having poles, and the notion is borrowed from 

 the phenomena of common magnets. Now if the particles of a 

 body possess polarity, it is obvious that they can unite with each 

 other only in one way ; so that irregular crystals and regular 

 crystals are formed precisely in the same way. The only differ- 

 ence between them is, that in the one case we perceive the 

 regular shape of the ciystal ; while in the other case that shape 

 is concealed. It is quite obvious that in calcareous spar the 

 particles of the carbonate of lime are arranged precisely in the 

 same order as in the most regular crystals of limestone ; for the 

 fragments are all rhomboidal, and exhibit the very angles which 

 exist in the primitive crystal of that mineral. I believe this to 

 be the case in all foliated minerals. Indeed Mr. Daniel has 

 shown it to be so in a variety of unexpected instances. The 

 reason why the regular shape does not appear to the eye is the 

 particular state in which the crystallization has taken place. 

 When a liquid matter becomes rapidly solid, or when it fills the 

 whole space in which it exists, it is impossible for the regular 

 form to appear to the eye ; because the different crystals are 

 entangled in each other, and fill up all the interstices between 

 each other. Radiated and fibrous minerals are in the same 

 circumstances as foliated minerals. The only difference between 

 them is in the breadth of the plates. When the plates are as 

 broad as the mineral, it is said to be foliated; when several plates 

 are required to make up the breadth, it is said to be radiated ; 

 and when the breadth of each p'.-.te is very small compared to its 

 length, it is said to be fibrous. Hence the observations made 

 with regard to foliated minerals apply likewise to radiated and 

 fibrous minerals. 



With regard to Delametherie's notion, that sandstone, chalk, 

 plants, See. are crystallized, it is not necessary to say any thing. 

 When he applied the term to these substances, it is obvious that 

 he affixed to it a meaning different from that which it commonly 

 bears. He seems to have considered chemical affinity, or 

 attraction of cohesion, to be all that was necessary to constitute 

 a crystal ; but a crystal in common language always is a sub- 

 stance formed into a regular shape, and of course composed of 



