The Rocks of Sark, Herm, and Jetlxou. 141 



2. " The Rocks of Sark, Herm, and Jethou." By Rev. E. Hill, 

 M.A., F.G.S. 



The author described the island of Sark, about three miles long by 

 two broad, with the smaller areas of Little Sark and Brecqhou. 

 Little Sark is attached to Great Sark by a narrow ridge (the Cou- 

 pee), which the weather is rapidly degrading, while Brecqhou is 

 completely separated by a narrow strait. The greater part of these 

 islands consists of dark hornblendic banded rocks, which closely re- 

 semble those of the Lizard, and show by their alternation of 

 materials and their phenomena of current-bedding that they have 

 originated by some kind of deposition. These were shown to lie un- 

 conformable' on a gneiss, seen only at the eastern extremity of the 

 island, in and around the Creux Harbour. Over this the beds lie 

 in a dome, and as they slope away on the N., W., and S., they pass 

 under a highly-crystalline rock, which has been called a metamorphie 

 gneiss. This rock was described, and evidence given to show that it 

 is really a granite, — an igneous rock which has overflowed the horn- 

 blendic beds. 



Yeins and dykes were briefly noticed ; they include a dyke of mica- 

 trap. The islands of Herm and Jethou, lying between Guernsey 

 and Sark, were also described. Jethou contains a fine raised beach. 

 They consist of granite which presents signs of an E. aud W. dip. 

 A probability was shown that this granite is part of the mass overly- 

 ing Sark. 



Finally the age of these rocks was shown to be Archaean, and at- 

 tention was called to the evidence they give that some at least of the 

 Archaean rocks did not originate out of igneous masses by crush, 

 but were formed by some process which, if not aqueous sedimenta- 

 tion, at all events was some kind of successive deposition. 



3. " Quartzite Boulders and Grooves in the Roger Mine at 

 Hukinfield." By James Radcliffe, Esq., F.G.S. 



Quartzite boulders have from time to time been found imbedded 

 in the roof of the Roger Mine coal-seam. Similar boulders had 

 previously been described from coal-seams both in Leicestershire 

 and the forest of Dean. The composition of the Roger-Mine boulders 

 was shown by notes furnished by Prof. Bonney to be quart/.ose grit 

 and quartzite, containing some grains of felspar, epidote, and tour- 

 maline and flakes of mica. This composition resembled that of 

 some of the pebbles in the Bunter conglomerate of the Midland 

 counties, and also that of some of the Loch Maree quartzites. The 

 boulders varied in weight from 166 pounds to 4 pounds, and ap- 

 peared to have been dropped into the coal, one boulder having been 

 found standing edgeways. They were half imbedded in the seam, 

 half enclosed in the overlying grey shale. 



In the upper surface of the coal in the same mine, grooves were 

 found running about S. 50° E., the mean direction of faults, slips, 

 &c, being S. 26° W. The sides of these grooves were raised, as if 

 by pressure, and each depression commenced as a small groove, then 

 increased in depth and breadth, and finally died out. 



