Correspondence — Mr. T. Stewart. 133 



As I do not intend to reply to any further statement on this sub- 

 ject, I hope the correspondence may now be considered as closed. 

 Geological Survey Office, 



Dublin, 9 January, 1882. EdwAKD HulL. 



THE GLACIATION OF THE SHETLAND ISLANDS. 



SiK, —With your permission, I should like to say a few words 

 regarding the discussion which has been carried on during the last 

 year in various numbers of the Geol. Mag., as I visited part of 

 Shetland in the summer of 1880, and although I went there chiefly for 

 mineralogical purposes, I also noted some of the glacial phenomena. 



The unequal distribution of the Boulder-clay on the sides of Dales 

 Voe is a striking fact, for while the northern slope is covered with a 

 considerable thickness of clay and has a smooth grassy surface half- 

 way up the ridge, the southern slope is bare, and presents mammil- 

 lated hummocks of rock. Noithwards from this point the whole 

 tract of country has a peculiar ice-wo^rn aspect; but on account 

 of the rocks being mostly of a schistose nature, they do not afford so 

 striking evidence as to the direction of the ice-flow. However, I 

 noted a few striae pointing nearly N.E. and S. W. 



Near Busta Voe a tract of diorite occurs-, and on this tract 

 numerous erratics occur, similar, so far as I could determine, to 

 the micaceous and gneissose rocks which lie to the north-east. 

 Further north, in the neighbourhood of Isleburgh and Sulem Voe, 

 the rocks have been very much worn, and in many places show 

 bare hillocks of rock moulded off into flowing outlines and covered 

 with scratches. Near Pondswater Loch the striag on an average 

 point W. to W. 10 S., and in the same locality boulders of gneiss, 

 schist, and granite are common. Further north, but still on the 

 diorite area, there are numerous boulders of gneiss and schist, but 

 1 was unable to discover any of granite. If we assume that the 

 ice-sheet came from the eastward, the fact is accounted for, because 

 there would be no granite in the tx*ack of the ice. On the small 

 patch of metamorphic schists at Hillswick I saw several boulders 

 of diorite, and as there is no diorite known to exist on the west 

 side of Hillswick Bay, there is every probability that these boulders 

 were carried across the Bay, but the most conclusive proof that such 

 has been the case is afforded by a fine section of Boulder-clay lying 

 in a hollow to the west of Hillswick. The lower part of this is 

 entirely composed of the debris of the schists on which the clay 

 rests, while the upper part is largely composed of blocks of diorite 

 and a few of the other rocks which lay in the path of the ice-sheet. 



The areas south of Ronas Voe and west of Hillswick show that 

 blocks of schist have invaded the felsitic area, while blocks of these 

 have in their turn invaded the porphyrite area. I looked for 

 porphyrites to the east of the fault which cuts them off from the 

 felsitic granite, but found none. 



Mr. Milne Home seems to have misapprehended a great deal of 

 Messrs. Peach and Home's evidence regarding the dispersal of the 

 stones in the Boulder-clay in the northern part of the mainland, for 



