of the Shetland Islands. 67 



I have seen cause to alter my opinion as to the direction of the 

 drift over Shetland, viz. the opposite of what I inferred in my paper 

 to the Royal Physical Society. At the time I Avrote (1864), I was 

 much puzzled, when examining the Boulder-clay near Hammer in 

 Balta Sound, to find -mingled with the striated stones of serpentine, 

 numerous striated stones of gabbro from Balta Island ; and then at 

 the haunted burn of Watlea, where the black shales are exposed and 

 in which lies the Boulder-clay containing smoothed and striated 

 stones of serpentine in abundance, when beyond the Skaw to 

 Saxaford Hill I met with no trace of serpentine or gabbro stones, 

 although I searched rather carefull3^ I now feel quite satisfied, 

 that although I noticed the bearing of the strige right, I was wrong 

 as to the direction the drift came from. At that time I was full of 

 dredging matters, and my mind ran so much after Hydrozoa, 

 Polyzoa, Crustacea, Mollusca, etc., that I had little time for examin- 

 ing the glaciation of the islands, and hence the oversight and neglect 

 of the warnings of Hammer and Watlea, for which I am sorry." 



The candid admissions contained in this letter enable us to 

 account for the discordance between the recorded observations of 

 Mr. 0. W. Peach, in 1864:, and ourselves. We visited the locality at 

 Hagdale, referred to by Mr. Peach, sen., and confirmed the accuracy 

 of his observations so far as the magnetic readings are concerned. 

 When due allowance is made for the magnetic deviation, the true 

 direction of the ice-flow at Hagdale is nearly E. and W., as noted by 

 us. Along the eastern seaboard of Unst. however, the stride vary 

 from W. to W. 80° S. ; the westerly trend being more prevalent in the 

 northern part of the island. From the foregoing letter it is also 

 evident that Mr. C. W. Peach had observed certain facts connected 

 with the dispersal of the stones in the Boulder-clay which un- 

 questionably point to the westerly movement of the ice. He noted 

 the occurrence of gabbro stones from Balta Island in the Boulder- 

 clay at Hammer, and striated serpentine fragments in the Boulder- 

 clay at Loch Watlea to the west of the serpentine area. These facts 

 are not referred to in any of the papers which he wrote on the subject 

 at that time, doubtless for the simple reason that they are inexpli- 

 cable on the hypothesis which he then adopted of an ice-movement 

 from the W.N.W. and N.W. Had he found time, in the midst of 

 his dredging operations, to traverse the western shore of Unst, 

 between Woodwick and Belmont, he would have met with still more 

 convincing proofs of this westerly movement in the presence of 

 serpentine and gabbro stones in the Boulder-clay, which must have 

 been carried across the water-shed. Indeed, so abundant are these 

 striated fragments in this deposit on the west coast, that it is im- 

 possible to escape the conclusion, that the ice must have crossed 

 Unst from the North Sea to the Atlantic. 



In 1868, Mr. C. W. Peach informed Dr. CroU ' that a minute 

 examination of the shelly Boulder-clay of Caithness, continued for 

 several years, had led him to the conclusion that the ice must have 



1 Geol. Mag. 1870, p. 212. 



