364 B. N. Peach ^ J. Some — Glaciation of the Shetlands. 



IV. — The Glaciation of the Shetland Isles. 



Eeply to Mr. Milne Home's Criticisms in the May Number of the Geol. Mag. 



By B. N. Peach, F.R.S.E., F.G.S. ; and 



John Horne, F.R.S.E., F.G.S. 



IN the May Number of the Geological Magazine, Mr, Mihie 

 Home expresses anew his doubts about our conclusions on the 

 glaciation of Shetland, laying special emphasis on the discordance 

 between the statements of Mr. C. W. Peach and ourselves. He also 

 cites Dr. Hibbert and Mr. Eussell as to the position of certain 

 boulders which, he considers, are at variance with our conclusions. 

 In his recent criticisms, Mr. Milne Home still displays a curious 

 misapprehension of many of the facts bearing on this question ; 

 besides he has committed a serious error in making allowance for 

 the magnetic variation, on the strength of which he tries to establish 

 a discordance between the trend of the ice-markings as given by 

 Mr. C. W. Peach and ourselves, in Unst and the Outskerries of 

 Whalsay. , 



We now desire to show (1) that there is no discordance between 

 the trend of the ice-markings recorded by Mr. Peach and ourselves 

 in Unst ; (2) that the supposed ice-movement from the hills in the 

 north of Unst against "the W.N.W., end " of the Heog Hill, which 

 was advocated by Mr. Peach in 1864, and now abandoned by him, 

 is completely disproved by the direction of the stride, and more par- 

 ticularly by the dispersal of the stones in the Boulder-clay in that 

 neighbourhood ; (3) that there is no discordance between the direc- 

 tion of the striae recorded by Mr. Peach and some of those noted 

 by ourselves in the Outskerries of Whalsay ; (4) that with the 

 exception of the blocks of actinolite schist on Papa Stour, which, 

 according to Hibbert, could only have come from Hillswick, the 

 various erratics cited by Mr. Milne Home may be satisfactorily 

 accounted for by the theory advocated in our paper. 



1. In our previous communication, we published a letter from 

 Mr. C. W. Peach, in which he stated explicitly that no allowance had 

 been made for magnetic variation in his observations, which 

 accounted for the discordance so far as the mere trend of the ice- 

 markings is concei-ned. With reference to this point Mr. Milne 

 Home says, "Messrs. Peach and Horne, commenting on this letter, 

 observe, that when allowance is made for magnetic variation, Mr. 

 Peach's bearings would be not W.N.W. as stated by him, but 

 'nearly E. and W. as noted by us.' This remark I don't under- 

 stand ; for as the compass in Shetland in the year 1864 stood 24° to 

 the west of true north, Mr. Peach's observations by true bearing 

 indicate N.W., and not due E. and W." 



Mr. Milne Home has here committed an error in his calculations 

 amounting to about 46°. The error is perfectly obvious to any one 

 who gives a moment's thought to the subject, but we have made the 

 following calculations to make it transparent at a glance. In 1864 

 (the year in which Mr. Peach, sen., visited Shetland) the compass in 



