369 MINERAL0GY. 



Mineralogy Qf gneiss. This roek constitutes the coast as far as hurra 

 Shetland. Frith, a bay very bold and broken on the cast side, where 



there is a hollow called Saxe's Kettle. It is formed by 

 an enormous mass, that seems as if separated fiom the 

 Mainland, and afterwards joined at Us extremities by the' 

 tailing in of less masses. In bad weather the m avcs are 

 driven with violence through a small opening toAvard the 

 bottom, and fill the whole yawning chasm with foam. 



The hills that lie between Norwick Bay and Burra 

 Frith are composed to the top of the striated micaceous 

 schistus above mentioned ; and, though the highest oa 

 the island, are covered with coarse grass and mosses, 

 while the serpentine ones, though inferior in iHjight, are, 

 for the most part, destitute of vegetation. Does not 

 this imply the hostile nature of magnesian earth to plants 

 in general ? 



At the bottom of Burra Frith, the same kind of undu- 

 lated micaceous schistus, before seen near Scalloway, 

 again presented itself. From Burra Frith, the coast 

 westward is composed of gneiss and micaceous schistus. 

 At HermanesSj the latter rock abounds, and often con- 

 tains finely crystallized garnets of a large size. Saw one 

 at a gentleman's house found there, which was nearly l^ 

 inch in circumference, beautifully crystallized, and of a 

 pretty good colour. At Hermaness are said to be grand 

 caverns, into which the tide flows, and which contain 

 fine natural pillars. These pillars are conjectured by 

 Mr. Jameson to be of gneiss. The heavy surf prevented 

 me from exploring these caverns. Toward the south, the 

 isle of tJnst is less bold on its shores, and the rocks 

 above described are succeeded by argillaceous schistus 

 and sandstone. In crossing the island to Mrs. B.'s, find 

 in the declivities plenty of bog iron-ore, and in one or 

 two places both earthy and schistose chlorite. 



The little island of Balta^ forming one side of Balta 

 Sound, is composed of serpentine of various shades of 

 colour. 



Sail for Lerwick : pass the bold coasts of Yell and 

 Fetlar, and sail between Out Skerries and Whalsey ; (for 

 an account of these see Professor Jameson's Outline). 

 Sail close under the stupendous Noss Head, a grand pro- 

 montory 



