540 TEOCEEDTNGS OF THE GEOLOGICAL SOCIETY. [June 25, 



Owing to the abundant presence of gneissic grit in the till, this 

 deposit weathers rapidly ; and the face of a section must soon become 

 concealed behind a curtain of coarse-grained gritty sand. For the 

 same reason, the decomposition and breaking up of the till all over 

 the country often gives to the ground the appearance of being 

 sprinkled with morainic debris. I satisfied myself, however, that 

 this moraine-like matter was merely the weathered upper surface of 

 the till, or the wreck of that deposit commingled with the debris of 

 the underlying gneiss. 



Some interesting sections of till are obtained along the south-east 

 coast of Eye Peninsula, near the village of Phabaill. Here it forms 

 in places an irregular terrace sloping to the sea. In other places 

 in the same neighbourhood it lies in hollows between the cliffs, or is 

 scattered over the hill-sides. We get it also on the very crest of the 

 lofty sea-cliffs themselves, where it occasionally attains a considerable 

 depth. Examples of this occur at Bagh Phabaill Iosal and at Lea- 

 baidh a Mhinisteir, near the Chicken Head, at which last-named 

 locality a bed of rolled stones underlies the till. Here also the 

 highly weathered and decomposed character of the gneiss below the 

 drift is well seen. 



Along the courses of such streams as cut down through the thick 

 peat good sections of till are frequently exposed. It is perhaps 

 hardly worth while to refer to any special example ; yet mention may 

 be made of the Gleann Mor Barabhais and some of its small tribu- 

 tary streams, as, for instance, Roundograth, where an excellent 

 exposure of till is seen, a little above where the road crosses the 

 water. The Amhuinn a Ghlinn Diubh, the Amhuinn Ghriais, and 

 the river Laxdale also show similar cuttings. But the geologist 

 need never stray far from the roads for good opportunities of study- 

 ing this kind of drift. He will find it laid open in numerous holes 

 and pits in every part of the island, where it is used for making 

 and repairing the roads — a use to which the much more argillaceous 

 till of the Scottish Lowlands could not be put. 



As far as my observations went, the bottom till did not seem to 

 form any distinct feature in Lewis. It appears to lie thickest in 

 the valleys and in sheltered hollows, especially in front of such 

 knolls and broken escarpments as face to the north-west. Occa- 

 sionally, however, it sprinkles the surface of exposed hill-slopes. But 

 the low-lying flats are usually so thickly covered with peat that the 

 configuration of the drift is entirely concealed. In some valleys I 

 thought I could detect a terrace-like arrangement of the till similar 

 to that which is so characteristic a feature of the Peeblesshire till. 

 Thus along the Amhuinn Theidagul, near Carloway, the till seen 

 from a little distance appeared to form a terrace sloping with the 

 slope of the valley, and dipping gently in towards the stream ; but 

 a nearer inspection, if it did not quite dispel, certainly rendered 

 this appearance much less conspicuous. 



In the north of Lewis there occur two more recent deposits of 

 stony clay, the lower of which is fossiliferous, and separated from 

 the upper by beds of gravel, sand, and clay, also containing fossils ; 



