392 PEOCEEDINGS OF TKE GEOLOGHCAL SOCIETF. [DeC. 1> 



The most remarkable exhibition of the flaglike gneiss with a 

 persistent and uniform dip is seen on the western cliffs of the island 

 of Unst, where the strata, in precipitous cHffs 200 to 300 feet high, 

 succeed each other rapidly at angles of about 45°. In the Burra 

 Fiord of the same island, granite prevails in strong veinstones, as also 

 in the islets called the Burra Fiord Holms. It is on the outermost 

 of these bosses of barren gneiss that the new lighthouse was erected 

 duriag the recent Bussian War ; the summit of the rock is 230 feet 

 above the sea, and exposed to the lashings of the wild Northern Ocean. 

 This rock (named the Muckle Flugga, to distinguish it from a more 

 southern boss, the Little Mugga), with the exception of a small 

 rock called the Out Stack, is the northernmost point of land ia Her 

 Majesty's dominions, and certainly the most northern iahabited spot ; 

 it is very nearly on the 61° of N. lat. 



The rock, up the steep face of which 250 steps are cut, by which 

 we ascended to the lighthouse, consists of sharply inclined shelving 

 masses of gneissose, micaceous, and quartzose flagstones, with some 

 garnets : it is penetrated by many veins of granite. The strata, like 

 those of Unst, dip E.S.E. about 45°, and are all perfectly parallel, — a 

 circumstance the more to be wondered at when it is seen that from 

 Somburgh Head on the extreme south to the Muckle Mugga on the 

 extreme north of the whole group, the prevalent strike and dip are 

 preserved for a distance of eighty miles. 



In Balta Sound a visit was made to the mines of chromate of 

 iron, much opened out and extended of late years. This mineral 

 occurs in serpentine rocks with bosses of pure greenstone. Followitig 

 up certain veinstones on the surface from the north side of the Fiord 

 between Swenee Kess and Buness, the mineral has been found to 

 expand into a large stockwork, about one mile from the shore : the 

 chief direction of the mineral mass is from W.S.W. to E.N.E. There 

 the rock is cut into to a depth of about 86 feet, without detecting 

 any deterioration or diminution of the chromate in the floor of the 

 quarry, which is from forty to fifty feet wide. This mineral mass hades 

 to the north at an angle of from 70° to 80°, and is situated on the 

 hill called Keen Hill, and at the foot of the higher rocky hills called 

 Heysags, which stand out so boldly, overlooking Haroldswick Bay. 



The other tract where I had an opportunity of studying the cry- 

 stalline rocks, was at the Out Skerries of Whalsey, that very singular 

 group of low, rugged islets, chiefly composed of gneiss with granite- 

 veins, but containing one strong band of limestone. It is on the 

 most eastern of these rocks, or the Bound Skerry, that a new light- 

 house has been just erected, to exceed in power that of the adjacent 

 Gruna Light*. 



Mr. Stevenson here called my attention to the manifest proofs of 



* After passing the afternoon upon the rocks, or in admiring the new mecha- 

 nical contrivances in the lanterns of the lighthouse, we steamed out to the north 

 about ten miles in the dark, to test the effect of one of the improvements made 

 by our companion, Mr. Stevenson, when it was perceptible to all of us that the 

 new Hght was very superior to the old one on the adjacent rock of Grruna, in the 

 grander and more pyramidal flashes which it gave out. 



