169 



Museum d'Histoire Naturelle de Paris. 8vo. — From the 



Museum. 

 Berichte iiber die Verhandlungen der Kbniglich Sachsischen Gesell- 



schaft der Wissenschaften zu Leipzig. (1848.) 870. Bande 



I., II., III. — From the Society. 

 Catalogue des Manuscrits et Hylographes Orientaux de la Biblio- 



theque Imperiale Publique de St Petersbourg. 8vo. — From 



the Russian Government. 



Monday, 7th February 1853. 

 Br CHRISTISON, Vice-President, in the Chair. 



The following Communications were read : — 

 1. On the Structural Characters of Rocks. By Dr Fleming. 



While the condition oP the mineral masses in the neighbourhood 

 of Edinburgh furnish interesting illustrations of the structural cha- 

 racters of rocks, such as the columnar, the concretionary, and the 

 fragmentary, «&c., the author proposed to confine his remarks at 

 present to what he denominated the Flawed Structuke. 



In the ordinary language of quarriers, the flaws are termed backs, 

 while they are known to masons as dries, and to geologists, when re- 

 ferred to, as slicken-sides. This last term, independent of its provincial 

 character, refers to one peculiar form of the flaw only, and, although 

 explicable according to the same views entertained respecting the 

 origin of the others, is far from being a typical form. The flaw of 

 the lapidary, in reference to crystals or gems, comes sufficiently near 

 in character to justify its adoption. 



The Flaw is a crack which is confined to the stratum or bed in 

 which it occurs, and is thus distinguished from fault or dislocation, 

 since these extend through several beds. It occupies all posi- 

 tions in the bed, without an approach to parallelism, the flaws being 

 variously inclined to one another, and not extending continuously 

 throughout the thickness of the bed ; thus differing from the columnar 

 structure. 



These flaws are sometimes isolated ; in other cases two unite at 



