1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



crystalline rocks were overlaid by horizontally or nearly horizontally- 

 stratified sedimentary deposits, the latter exhibited at their point of 

 contact with the older rocks evidence of undergoing the process of 

 vertical cleavage or lamination, and that the lines of stratification 

 were gradually obliterated. Mr. E. Hopkins does not, as far as I 

 can understand, draw any distinction between cleavage and lamina- 

 tion. 



Mr. Sharpe, avoiding the universality of Mr. E. Hopkins, confined 

 his remarks to those portions of the chain of Mont Blanc which he 

 had visited during the past summer. Having disposed of the erro- 

 neous views of former authors, who, not sufiiciently attending to the 

 differences of stratification and cleavage, had asserted that the gneiss 

 or stratified granite of Mont Blanc overlaid the secondary rocks seen 

 in the Valley of Chamounix and in Val Ferret, Mr. Sharpe pointed 

 out that the chain of Mont Blanc consists of two lines of vertical 

 foliation, about one mile and a half apart, having a strike parallel to 

 the major axis of the chain, extending alon^ its whole length, and 

 separated by a narrow anticlinal axis. This anticlinal axis, how- 

 ever, appears to me to be the result of the fan-shaped arrangement 

 of the two systems of radiation. The planes of foliation, which are 

 vertical along the highest ridges of the mountain, radiate as it were 

 outwards as they recede from the central vertical line. Thus, 

 where there are, as here, two lines of foliation running parallel to 

 each other, the southern radiations of the northern line diverge to- 

 wards the northern radiations of the more southern line, and thus 

 produce the appearance of an anticlinal axis. Mr. Sharpe also 

 pointed out that where the crystalline rocks are overlaid on their line 

 of strike by slates of sedimentary origin, the cleavage of the slates 

 is on the continuation of the planes of foliation of the gneiss and 

 mica schist, and that where the slates lie against the sides of the 

 crystalline mass, their cleavage planes combine with the planes of 

 foliation of the crystalline rocks to form anticlinal axes of considerable 

 regularity ; thus confirming the opinion originally pronounced by 

 Mr. Darwin, and subsequently confirmed by Mr. Sharpe himself, by 

 observations in the Highlands of Scotland, that the cleavage of the 

 slates and the foliation of the crystalline rocks were owing to the 

 same cause. 



The observations contained in Mr. D. Forbes' s paper derive addi- 

 tional importance from the many opportunities the author has had 

 of studying the structure of the crystalline rocks in Norway and else- 

 where, and from the corroborative evidence he has acquired in pro- 

 ducing artificial gneiss out of clay-slate by long exposure to great 

 heat, but not at such a degree as would produce fusion. Mr. Forbes 

 insists strongly on the difference between cleavage and foliation, con- 

 sidering cleavage to be the result of mechanical action, whilst folia- 

 tion can only be accounted for as the result of chemical forces, but 

 not necessarily requiring such a temperature as to produce fusion, or 

 even semi-fusion. The following views are considered by Mr. D. 

 Forbes as the result of his inquiries : — 1 . That foliation and cleavage 

 are two distinct processes not necessarily connected ; 2. That foliation 



