mu-ian.j 44 g 



Mr. R. J. Welch, M.R.I. A., pointed out that whilst the 

 discussion had been very interesting, it did not help definitely to 

 solve the problems of dispersal, but that many interesting points 

 had been raised which should stimulate further research. 



Messrs. C. M. Cunningham, L.D.S., and H. L. Orr also 

 spoke. 



A TALK ON LIMESTONE. 



A meeting of the Geological Section was held on 15th 

 March, at which Mr. William Gray submitted a communication on 

 " Limestone," one of the materials of which the crust of the globe 

 is composed ; and of which there are two main classes — the 

 igneous and the sedimentary. The former originated by volcanic 

 agency and the other by marine or mechanical agency resulting in 

 sedimentary or stratified deposits. Limestone belongs to the 

 mechanical group and has been accumulated mainly by marine 

 agency. It occurs in every geological age and has a wide range of 

 geographical distribution, and is nowhere relatively more abundant 

 or varied than in Ireland. 



Although limestone occurs mainly as a marine or stratified 

 rock it is not entirely absent from igneous rocks : it occurs in the 

 mineral mica, which is one of the minerals of which granite is 

 composed. The term limestone explains itself — a stone formed 

 of lime — for which purpose it is combined with carbonic acid ; 56 

 of lime and 44 of carbonic acid. 



The primary crystal of limestone is a rhomb having a curious 

 property called cleavage, by which it splits up in definite lines, 

 assuming the same definite form no matter what the size of the 

 specimen may be. The combinations of similar crystals are cap- 

 able of producing as many as 700 compound forms of great variety 

 and beauty, yet if any one is selected and crushed to the finest 

 powder and examined under the microscope the cleavage planes of 

 the fragments will show the cleavage planes of the original rhomboid 

 crystal. It was the discovery of this cleavage property early in the 

 last century that originated Crystallography and raised it to the 



