626 



SCIENCE. 



on a terrace in a cemetery at Augusta, Me. "On this terrace 

 snow accumulated one winter so as to fill up the re-entrant 

 angle it formed with the hill-side. When in the spring this 

 snow melted away, it was found that the upright tomb- 

 stones and the iron fence that surrounded the graves were 

 broken off near the surface of the ground, and moved in 

 the direction of the general slope of the hill" (p. 148). 

 Summing up the foregoing hypotheses in their application 

 to glaciers of the alpine type, and viewing them in the 

 light of the various phenomena recorded, it appears that 

 all except the sliding and viscous theories are "true causes" 

 of ice-motion ; and though neither is alone competent 

 to explain the various phases of the movement, all must 

 be recognized in a satisfactory and consistent theory. As 

 in the theory framed to account for glacial periods, so in 

 this case also, our theory is sufficiently flexible and indefi- 

 nite to be sure of coinciding with the truth in some of its 

 aspects. 



" The problem with which we have to deal when we 

 come to the task of explaining continental glacieis is of 

 quite a different nature " ( p. 1 5 1 ), since in this case " we 

 have to leave gravity, as it works in Swiss glaciers, almost 

 out of account " (p. 1 54 ). The ice might move freely for 

 a score of miles from its sou'hern border; but in the in- 

 terior little if any motion would probably occur, except 

 such as might result from pressure-melting; the excess 

 of water formed in this manner escaping in sub-glacial 

 streams. " In this way we may conceive that the ice of 

 British America may have been carried out, from centre 

 to periphery, in the form of water, and the waste of its 

 grinding borne along by the streams that were formed by 

 the pressure-melted water " (p. 159). In other words, 

 continental glaciers appear not to move as ice, but only 

 as water, exctpt along their extreme peripheries. 



XIII. Certain effects of glaciers. — Outside of glaciated 

 regions the soils and sub-soils are the products of simple 

 weathering conjoined with vegetal action, and may be de- 

 nominated soils of immediate derivation : while within 

 such regions the superficial accumulations are made up 

 of mechanically comminuted materials brought thither 

 from numberless localities, some perhaps hundreds of 

 miles distant, and may be termed soils of remote deriva- 

 tion. Since the soils of the first class vary with the char- 

 acter of the underlying rocks, it follows that the latter are 

 more uniform in constitution over considerable areas ; 

 and they are at the same time more durable, for not only 

 are the materials essentially identical in all parts of the 

 thickness of the deposit, but they also contain desirable 

 mineral constituents locked up in the included pebbles to 

 be gradually liberated by atmospheric and chemico-vege- 

 tal action. The glacial clays were "laid down in a very 

 unoxidized state. Generally they are of a bluish hue, 

 and only attain the ordinary yellowish or reddish color 

 of decomposed clays as the waters acidulated by vegeta- 

 tion slowly penetrate into them." " In North America 

 this penetration of atmospheric decay is distinctly pro- 

 portionate to the nearness of the clays to the old glacial 

 front " ( p. 165 ) ; and hence affords a rough measure of 

 the length of post-glacial time. 



The coarser moraine debris constitutes, however, but 

 a small part of the glacial waste ; — the impalpable glacial 

 mud must have been formed in scores if not hundreds of 

 times its volume, and swept for the most part into the sea 

 to build up azoic shales and clay slates, perhaps interco- 

 lated with conglomerates, as in the Roxbury conglome- 

 rate series near Boston. This fine glacial detritus, 

 whether accumulated in river-beds, lake-bottoms, or un- 

 fossiliferous marine formations of any age, may be dis- 

 tinguished from river salt by its unoxidized state and blue 

 color. The distribution of both the coarser and the finer 

 glacial products has been largely accomplished by ma- 

 rine forces, after they were thrust by the ice into the sea ; 

 as in the case of the Tertiary sands of the southern states, 

 which were probably originally brought to the ocean 

 by glaciation along the more northerly Atlantic coast. 



The formation of auriferous gravels and the general 

 accumulation of gold in drift by glacial action, was ac- 

 complished by the simple concentration of heavier ma- 

 terials in depressions or gentle slopes, just as occurs in 

 miniature in a miner's pan or rocker; and the result may 

 be brought about by local as well as general glaciation, 

 as is well shown in the valley of the Arkansas River at 

 Twin Lakes. 



" It is a very important fact that no pre-glacial caverns 

 have ever been discovered" (p. 170)— a fact which leads 

 to the inference that the extent of glacial erosion was so 

 great as to totally remove pre-existing cavern-bearing 

 hmes'one strata. The excavation of fiords and lake- 

 basins, already adverted to, is a farther illustration of the 

 enormous extent of this erosion. A most interesting, 

 though indirect, result of this property of glacier ice is 

 the influence which it has exercised on the social condi- 

 tion of mankind ; for it is only shores indented by bays, 

 fiords, and inlets, and fringed with islands, that afford 

 the incentives to and facilities for the development of the 

 maritime industries which occupy so important a place in 

 human progress. The far-seeing geologist cannot, how- 

 ever, avoid speculating on the possibility that a contrary 

 effect may, in the distant future, be exerted on mankind, 

 by the return of glacial conditions to our globe. There 

 is every probability, indeed, that the earth will again be 

 enfolded in an icy mouth such as crept over it during the 

 Quaternary ; though there is no reason to fear that such 

 an 1 untoward vicissitude is imminent. 



A glossary of some fifty terms, a bibliography of nearly 

 seven hundred entries, and a four-page index with the 

 plates and descriptions follow. 



It has been the aim to present, in the foregoing para- 

 graphs, a full synoptical resume 1 of the work considered, 

 without approval or comment. Several passages which 

 are regarded as either erroneous or misleading, or open 

 to serious objection on well-established theoretical 

 grounds, have, however, been quoted in the words of 

 the author. A portion of these may be noticed in 

 their order ; refereuce being made to the pages on which 

 they occur. 



P. 28. — Geikie 1 regards ice-bergs as the terminal por- 

 tions of glaciers, broken off by their buoyancy on enter- 

 ing the sea ; Tyndall, 2 however, supposes that the 

 masses break downward by their own weight ; while 

 Schwatka 3 has shown that they are formed in either mode 

 according to the temperature of the sea — and, he might 

 have added, other circumstances. 



P. 31. — " From information derived from all sources 

 up to the present time, it may be gathered that the un- 

 penetrated area of about 4,700,000 square miles sur- 

 rounding the South Pole is by no means certainly a contin- 

 uous 'Antarctic Continent,' but that it consists much more 

 probably partly of comparatively low continental land, and 

 partly ot a congeries of continental (not oceanic) islands, 

 bridged between and combined, and covered to a depth 

 of about 1,400 feet, by a continuous ice-cap ; with here 

 and there somewhat elevated continental chains, such as 

 the groups of land between 55 and 95 W., including 

 Peter the Great Island and Alexander Land, discovered 

 by Billingshausen in 1S21, Graham Land and Adelaide 

 Island, discovered by Biscoe in 1832, and Louis Philippe 

 Land by D'Urville in 1838, and at least one majestic 

 modern volcanic range discovered by Ross in 1841 and 

 1842, stretching from Balleny Island to a latitude of 78 

 S., and rising to a height of 15,000 feet." 4 



Pp. 38, 98.— Geologists generally do not consider that 

 the correctness of the views of Ramsey and others as to 

 the repeated recurrence of glacial periods throughout ge- 



1 " Great Ice Age," Am. ed., 1877, p. 55. 



2 " Forms of Water," 1877, p. 134. 



3 Science, vol. ii, No. 30, i88i,p. 31. 



4 Sir Wyville Thomson, in addresses before the Geographical Section ot 

 the British Association, Dublin meeting. Brit. Assoc. Rep., 1878, p. 

 619 ; Nature, Aug. 22, 1878 ; Am. Jour. Sci., vol. xvi., 1878, pp. 355-6- 



