86 PKOCEELINGS OP THE GEOLOGICAL SOCIETY. [DcC. 18, 



I am prepared to accept the substantial accuracy of the above 

 woodcut, with one important alteration. It is sufficiently obvious 

 that if " a " is the present summit of the hill, the old one must 

 have been somewhat higher, say at a', and the original slope con- 

 sequently steeper than a h. 



As regards the facts, then, we have a substantial agreement ; and 

 they may be summed up as follows : — 



1st. The side of the hill is covered with rubbish derived from the 

 weathering of the rocks. 



2nd. The roads are not excavations in, nor embankments on, the 

 side of the hill, but, in the words of Macculloch, resemble stairs, or 

 sections of parallel layers applied in succession to the face of the 



hm. 



3rd. The horizontal roads do not appear when the solid rock 

 appears, nor when the slope is exceptionally flat. 



4th. Macculloch only saw one case in which there was a superior 

 talus, and never found any trace of an inferior one. 



5th. The stones on the road are very little roimded. 



6th. The roads are quite continuous, except under the circum- 

 stances named above, or where a rivulet runs down the side of the 

 glen. 



7th. The roads slope towards the valley. 



8th. The roads are very equal in size. I^ot only is this the case 

 with each road during its whole course, but it is also true of them 

 as regards one another. 



9th. When, however, they are narrower they are also steeper 

 than usual. 



The true explanation of the origin of the roads must be consistent 

 with all these conditions. 



I now proceed to consider the various explanations which have 

 been suggested. 



It is not, indeed, necessary to consider the theory which regarded 

 them as literally roads made of old by Fingal and his brother 

 heroes — nor the more prosaic but scarcely less preposterous one, 

 that they were made for hunting-purposes by the early kings of 

 Scotland. 



Taking the principal authors who have written on the subject 

 in chronological order, we commence with Dr. Maccxdloch, who 

 thus explains how in his opinion the " roads " were formed. 



" The water," he says, " checks the constant and gradual descent 

 of the alluvia of the hills. The descending matters thus losing a 

 large portion of their weight by immersion in the water, and in 

 vrinter often rendered still more buoyant by being entangled in ice, 

 are thrown back against the face of the hill by the incessant action 

 of the superficial waves, and are thus evenly spread against its 

 side." * 



Sir T. Lauder Dickf gives a diagram of a lake with precipitous 

 banks, in which he supposes that the water would excavate a hollow. 

 If, however, the materials were sufficiently solid to stand at so 

 * Loc. cit p. .371. t Edinb. Roy. Soc. Trans, vol. ix. 



