Vol. 62.] STRUCTURE OP TILE SGURR OF EIGG. 61 



Tertiary rocks brought up from below by explosive action, and 

 these sometimes exceed the basalt itself in amount. In the present 

 case, the non-volcanic fragments that occur are such as might be 

 expected. The Oolitic sandstones underlie the basalt-group probably 

 a little below sea-level at this place, and below that we should 

 confidently expect a good thickness of Torridonian strata. Tho 

 occasional presence of flint, suggesting the presence of concealed 

 Cretaceous rocks, is of some interest ; for, on the coast some 2 miles 

 to the north, Mr. Tait has detected an exposure of Cretaceous sand- 

 stone containing flints. The larger blocks in the breccia show no 

 sign of arrangement by water-action, and the manner in which 

 fragments of a given rock tend to cluster in one place is much more 

 characteristic of a volcanic agglomerate than of a fluviatile deposit. 

 Most significant of all is the fact that here, as at Bidein Boidheaeh, 

 fragments of the strong dolerites are wholly wanting. This ean 

 only be interpreted as showing that the accumulation, whatever its 

 nature, is older than the dolerite-sills, and belongs to the basalt- 

 group, not to the epoch of the pitchstone. The visible relations at 

 this place are scarcely sufficient in themselves to determine whether 

 the deposit in question is interstratified in the basalt-group or 

 behaves with the overlying pitchstone ; but it is certain that no 

 corresponding breccia is to be seen at the base of the pitchstone on 

 the opposite side of the ridge. If, as the above evidence would 

 indicate, this fragmental deposit is interstratified in the basalt- 

 group, it should be found on the north side at some distance below 

 the base of the pitchstone, unless it has died out in the interval. I 

 sought it at this place without success. Dr. Peach, however, 

 detected signs of it on the north side of the Gualainn, or shoulder, 

 which forms the eastward prolongation of the Sgurr ridge. Here, 

 at the proper horizon but not elsewhere, are found on the surface 

 many small pieces of Torridonian sandstone mingled with the 

 fragments of basalt. These probably mark the occurrence of the 

 breccia at this place, but some excavation would be required to test 

 this point. 



On the river-gravel hypothesis the deposit should occur, if at all, 

 on the opposite (southern) side of the Gualainn ; and Sir Archibald 

 Geikie recorded an outlier of it here, resting against the denuded 

 edges of the basalts, the stones being much more rounded and smooth 

 than in the former locality. 1 Repeated search has not enabled me to 

 verify this occurrence. The only fragmental accumulation to bo 

 seen here is one of Glacial origin. It consists of dolerites and 

 basalts, with some quartz-porphyry and other foreign rocks, but 

 without Torridon Sandstone. These rocks occur as pebbles and 

 boulders up to a foot or more in diameter, more or less rounded, but 

 frequently planed, and sometimes showing well-marked striation. 



A distinct but related question is that of the true age of the 

 fossil wood. Sir Archibald Geikie regarded it as the remains of 



1 Quart. Journ. Geol. Soc. vol. xxvii (1871) pp. 307-308. 



