176 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 31, 



The cases already described show in some measure the wide range 

 and extraordinary difference in mineralogical or chemical composition 

 of the substances producing foliated structure ; and I think it must 

 be admitted that we have no such analogous phsenomena characteristic 

 of the cleaved rocks, and that these facts would be opposed to the 

 view that cleavage and foliation were the effects of one action. 



Mr. D. Sharpe, in his excellent paper " On the Foliation and 

 Cleavage of the North of Scotland*," has brought forward another 

 argument in support of the identity of these two phsenomena, namely 

 the arrangement of grand semicylindrical arches in which the lines 

 of foliation and cleavage together form the defining boundaries. 



My excursions in Scotland were too short to form even a faint 

 idea of these arches. It seemed to be not improbable, however, 

 that these lines, which appear so regular upon Mr. Sharpe' s map, 

 might be found continued into Norway, where I was better acquainted 

 with the rock-structure. I could, however, make nothing of them, 

 and must candidly confess that I relapsed into that state of despair 

 described by Mr. Sharpe as '* the first impression of an observer 

 entering a district of gneiss or schist in search of order in the arrange- 

 ment of their folia." The geological map of Norway now produced, 

 and which is by Keilhau, has indicated on it a resum^ of most ob- 

 serv^ations of strike and dip made in that country prior to 1849, and 

 probably more experienced observers than myself may be able to 

 reduce these lines to a system. I am sorry that time has not per- 

 mitted me to mark down on the map a great number of observations 

 made by myself or collected from friends, since its publication. 



In an attempt to generalize the lines of foliation in the district 

 around Arendal and Krageroe in an examination of that tract made by 

 Mr. Dahl and myself, and published last year in Norway t, we were 

 unable to come to any more definite conclusion than that these lines 

 generally varied from N.W. to E. and W., and were in the main parallel 

 to the line of coast. The dip was found extremely variable at all angles, 

 from 13° to 90°, S.E., S., up to S.W. Contorted arches are of 

 constant occurrence in the gneiss districts in Norway, but they seem 

 to be connected with local phsenomena. Some are very interesting, 

 and the arrangement shown in fig. 8 is one difiicult of explanation. 



(Case 13.) — We have in fig. 8 a section of a ravine near Krageroe 

 (the section being broken in the centre to admit of both sides being 

 shown, otherwise impossible from the scale) . The ravine at the bottom 

 is probably not 50 feet across, and the precipice of the side is about 

 60 feet high. The angles dip in opposite directions on the respective 

 sides of the ravine ; on the one side, N.W. at various angles up to 

 vertical ; on the other, pretty constant at about 60° S.E. The 

 dotted lines show what may be supposed to have been the continua- 

 tion of the jagged edges of the strata, and are confirmed by the 

 blocks of similar configuration lying loose in the ravine below. 



The central boss a represents a mass something between granite 



* Phil. Trans. R. Soc. London, 1852. 



t See also Quart. Journ. Geol. Soc, No. 42, Part II. Miscell. p. 9, &c. 



