1869.] NICOL PAEALLEL ROADS. 283 



corned in the special arguments for or against the two varieties of 

 the lake -theory. 



Whatever view we may take of the origin of these lines, one 

 great fact seems beyond dispute. Long before they originated, the 

 country in which they lie must have had nearly its present form 

 and outline — the same hills and mountains, the same glens and 

 valleys, with nearly their present relative elevations. This fact we 

 may, or rather must, assume in all our reasonings and speculations. 

 This region has also been subjected to a very extensive glacial 

 action. Wherever the rocks are newly exposed they are marked by 

 grooves and striae. The direction of these striae and the form of the 

 rounded rocks show that in a few cases the ice has come down some 

 of the lateral valleys and moved towards the "west. But other facts 

 appear to me to indicate that here, as in other parts of the North of 

 Scotland, the great ice-stream has flowed from the west, and pro- 

 bably from a lofty mountain- chain that then existed in that region. 



Subsequent to this ice-period, but before the formation of the 

 Glen-E-oy lines, the whole region has been submerged in the sea. 

 This is proved by the uniform coat of detritus covering the whole 

 surface, in a thicker or thinner sheet according to the form of the 

 ground. This coat is not the mere surface waste, but matter laid 

 down by water, and is too widespread and general in its distribu- 

 tion, and too much mixed in its composition, to have been formed 

 in any mere lake. Associated with it are numerous boulders of 

 travelled stones, some of them imbedded in its mass, others lying 

 on the surface. As examples of these I may mention some huge 

 blocks of black granite and other smaller masses of red porphyry 

 which occur within a few yards of the summit of Craig Dhu, a 

 conical mountain of mica slate, that rises to more than 2000 feet 

 above the sea, in the angle between the valleys of the Spean and 

 Roy. One block must weigh about forty tons ; and they are evi- 

 dently ice-borne masses, floated probably far from the west in the 

 ancient ocean. 



It is in this detrital cover that the lines are cut ; and the period 

 and mode of its formation are thus of much importance. That it is 

 a marine deposit seems beyond doubt. That it has been formed 

 since the general glacial striation of the land is also proved by the 

 fact that it spreads over the rocks marked in this manner. This is 

 well seen in the Spean valley in very many places. More convincing, 

 or at least more interesting, is the fact that in Glen Eoy these 

 striated rocks occur immediately under the lines. The old line or 

 parallel road now passes over the rock-surface that in a former 

 period was worn and striated by the glacier. There is thus the 

 most direct proof that the period of general ice-striation was sepa- 

 rated from that of the formation of the lines, by a period in which 

 the land was submerged in the ocean and its general cover of detri- 

 tus deposited. 



This fact, however, does not decide the mode of formation of the 

 lines, or even its relation to ice and glaciers. There is abundant 

 evidence in many parts of Scotland that the great western giaciation 



VOL. XXV. PAPvT I. X 



