278 Proceedings of the Boy at Physical Society. 



and the ice markings. Along tlie shores of Balta Sound the 

 boulder clay is a tough, blue and yellow, stony clay, packed 

 with stones almost entirely of serpentine. The larger blocks 

 are beautifully striated. On the low ground from Buness 

 towards Baliasta Kirk the same deposit is traceable at inter- 

 vals, occurring in irregular patches, and possessing the same 

 general character. At the south-east corner of the Loch of 

 Cliff the limit of the serpentine is reached. In a quarry 

 at the roadside near the head of the voe, grey decomposing 

 schistose rocks crop out on the right-hand side of section. 

 Reposing on these rocks on the left side of section, a thin 

 deposit of till is met with, crammed with serpentine stones. 

 Crossing the bridge which spans the Vallalield Burn, a little 

 way above Loch Cliff, at the road side, grey decomposing schists 

 are again met with ; and at the north end of section there is 

 an exposure of stiff, stony clay with serpentine stones, while 

 the clayey matrix is formed of the pounded-up schistose rocks 

 which lie underneath. About two hundred yards along the same 

 road running westwards toward a farmhouse, another quarry 

 is dug in stony boulder clay. The most of the stones in this 

 deposit likewise consist of serpentine, with a small proportion 

 of quartz rock and grey schist. About a hundred yards still 

 farther west, at the road side, there is a good exposure of 

 coarse micaceous-gneiss dipping E. 20 S., at an angle of 20^. 

 There is no drift seen in this quarry, but near this point on 

 both sides of the road there are small sections of boulder clay 

 with scratched stones. The small stones, and, in fact, the 

 clayey matrix, are made up of the underlying schists, but the 

 larger blocks about six inches long consist of serpentine. I 

 could find no serpentine in place in the neighbourhood, 

 except to the east of the Vallafield Burn, and it is evident, 

 therefore, that the ice which glaciated Unst must have crossed 

 the island from east to west, rolling its bottom moraine ivest- 

 wards from the area occiqned hy the serpentine, 07i to the track 

 of the gneissose rocks. 



We are led to the same conclusion by the evidence fur- 

 nished by the erratic blocks. In the valley west of Baliasta 

 Kirk, where the boulder clay sections above described occur, 

 blocks of serpentine can be traced at intervals westwards to 



