GEOLOGICAL FORMATION 67 



material in its downward course. Without considering its 

 rocky aspect, which possibly strikes the traveller from the 

 south as nothing short of remarkable, the predominating 

 note in the island's landscape is the flowing and undulating 

 outline acquired during the glacial period. It is true, 

 however, that the softer rocks are yielding to the 

 disintegrating influence of the weather, and that the 

 characteristic results of the ice are being slowly but surely 

 effaced. 



Rocks and Flora. Owing to the identical structure of 

 Coll, Tiree, and the Outer Hebrides, we would expect to find 

 their floras very much alike in composition. Such, in fact, 

 is the case ; but while Mr M 'Vicar, in his Notes on the 

 Flora of Western Inverness, classes Tiree with the Outer 

 Hebrides, he points out that the flora of Coll has many 

 features in common with that of the schistose islands. In 

 the actual records of plants there is a greater resemblance 

 between the floras of the schistose and gneissose islands than 

 between either of them and those of the basaltic formations. 

 It should be noted, however, that the soil in many of the 

 most prolific localities in the former has not been derived 

 from the rocks of which the islands are composed, but has 

 been deposited during the raised-beach periods. It is 

 probably of these raised-beach deposits that much of the 

 low-lying and most fertile land of the islands Coll, Tiree, 

 Barra, etc. is composed. 



A larger number of plants are found in the South Inner 

 Hebrides than in any of the other groups. The many other 

 kinds of rocks, besides the schists, entering into the struc- 

 ture of the islands may help to enrich their flora. Certain 

 calcicole plants are known to occur on the limestone in 

 Islay, and even in Colonsay, where the area occupied by this 

 rock is restricted to very narrow limits. The flora of 

 Lismcre is characterised by the common occurrence of 



