Reviews — Bryce's Geology of Arran. 655 



ceives siipport from tlie case before us. A crowd of lesser blocks 

 surrounds the huge boulder of which we speak, — an association 

 much more likely to occur in the case of glaciers or hergs than of 

 currents emanating from a centre so remote." Why, it did not 

 appear that he leant at all to the hypothesis of currents of water, — 

 it was condemned as " totally inadequate." Yet here we have it, 

 as it were, reprieved and brought back again, as a thing not so very 

 unlikely, but having only a balance of probabilities against it. Then 

 it appears, from what Dr. Bryce has just said, that the cause to 

 which he chiefly leaned was " glaciers or bergs." But on turning 

 back to the articles referred to, we find that after being " shut up to 

 the conclusion that the agent was ice in motion," he proceeded to 

 consider the " two ways in which this agency may have been brought 

 into play," viz. floating bergs, and land-ice or glaciers. And he 

 summed up in the following terms : " Our views formerly inclined 

 to the iceberg theory and submarine deposit of the blocks ; but a 

 recent careful examination," etc., "have led us to the conclusion that 

 the agency of floating bergs is insufficient to have produced the 

 regularity and persistency which the markings and other evidences 

 of ice action now present, and that an icy envelope in a state of con- 

 stant advance will alone explain them" (p. 43). After which it is 

 exasperating to have "glaciers or bergs" coolly classed together as 

 " the cause to which we chiefly lean." 



If Dr. Bryce's footing be thus unstable on the ice, we cannot say 

 that it is firmer or surer on the "Boulder-clay." At p. 44 he writes, 

 "The occurrence of recent shells of arctic species in the deposit 

 called the ' Boulder-clay ' shows that in Arran, as on the mainland, 

 a climate prevailed favourable to the development of glaciers." 

 But, as we learn afterwards, the shells do not occur in the Boulder- 

 clay, but in certain beds of clay and sand overlying it. The 

 Boulder-clay itself — "the true old Boulder-clay," as he elsewhere 

 states (pp. 183-4) — is, so far as he has yet found, unfossiliferous ; 

 and he properly warns those engaged in the study of these super- 

 ficial formations against " hastily assigning to the Boulder-clay — that 

 is, the lowest and oldest bed — shells or other fossils which may 

 really belong to those which are superior to it" (p. 189). Then, 

 the Boulder-clay, he is of opinion, " may have been formed by land- 

 ice ; the shell-bed over it, under and around a rim of ice when the 

 land had been depressed." The shell-clay is thus later than the 

 Boulder-clay, has been formed partly out of it, indicates a difi'erent 

 condition of the surface, and is on no account to be confused with it. 

 Yet, as we have seen, he begins by treating it as a part of the 

 Boulder-clay. 



Again, looking at the shell-beds in Arran, he finds their elevation 

 above the present sea-level to range from 70 to 180 feet ; " so .that 

 the greatest depression of which we have any evidence here is 

 180 feet below the present sea-level, not taking account of the 

 depth required for certain species ; and loe hesitate to speak with 

 confidence of any greater depression" (p. 190). But how does this 

 agree with what we find at p. 46, " That if we can trace an un- 



