;86 



NA TURE 



[August 24, 1893 



erode its base, sure'y miles of the very same mass of ice, 

 with the same mud and stones, when broken off and 

 driven by wind and current on a shelvinir shore, must 

 grind and polish the floor on which it is driven. 



It is difficult to follow the explanation offerei of the 

 pushing up of shells belonging to tenperate climates by 

 the great ice sheet, or the wrenching off of large masses 

 of rock underneath the ice, except ot\ the supposition 

 that all this vv,\s done during \\\^ first advance of the ice 

 over the sea bottom, and over a surface irregularly fretted 

 by subrerial action. When once the sea-bed had been 

 swept, no more such life would be there till the ice 

 receded ; and, when the crags had once been planed 

 down, there could be no more jagged rock for the ice to 

 break off and carry along. Moreover, it does not seem 

 to have been observed that the flints so universally dis- 

 tributed through the marine gravels, such as those of 

 Moel Tryfaen, are rusty gravel flints, and that there is no 

 long interval without them all round the southern and 

 central portions of the British Isles. 



The point, however, to which our author seems to attach 

 greatest importance is the occurrence of interglacfal 

 periods. He describes successive sheets of boulder clay, 

 each of which is the accumulation of a separate and dis- 

 tinct ice flow. He points out that the fauna and flora found 

 in beds inierstratifiedin these clays are suggestive of alter- 

 nations of cold and damp conditions with those indicative 

 of a warm and genial climate. In Scotland and Scandi- 

 navia the gradual disappearance of the latest ice-sheets 

 was, he says, marked by a partial submergence, but a great 

 submergence he does not believe in, and, after describing 

 the grand series of moraines which stretches across tlie 

 northern states of America into the British possessions, 

 sa; s that " no one who has traversed the regions I refer ' 

 to is at all likely to agree with Sir W. Dawson's view j 

 that the American mounds, &c., are the shore accumu- 

 lations of an ice-laden sea." 



We regret the somewhat assured manner in which the 

 views of those who differ from our author are dismissed. 

 Sir William Dawson traversed the regions referred to 

 by him (p. 190) and arrived at a different conclusion ; 

 and there are some who have not confined themselves so 

 exclusively to the subjects on which our author has made 

 himself a name, who yet do not deserve to be excluded 

 fro.n the list of geologists because they do not agree with 

 him on every point. It would be well also if he would 

 strike out from any future edition all references to " the 

 trained observer" and "the experienced eye," as his 

 readers cannot help recalling many instances where 

 trained observers have differed in interpretation, and 

 where, the position having been shifted, even the ex- 

 perienced eye has seen things differently at different 

 times. 



Though our author could not in these essays discuss 

 fully the various points which must be fixed before any 

 theory can be considered as fairly established, he has 

 indicated the lines of reasoning on which he would rely. 



His position seems to be that there are known to recur 

 such astronomical combinations as by a general lowering 

 of the snow line would be sufficient to account -for glacial 

 conditions with such distribution of land and water as for 

 instance prevail at present ; that with unfavourable geo- 

 graphical arrangement noglaciation is possible ; that the 

 NJ. 1243, VOL. 48] 



greater part of the results observed were produced by 

 land ice, icebergs playing quite a subordinate part, and 

 marine currents of any considerable volume and velocity 

 being quite exceptional ; that within each period of pos- 

 sible glaciation there were alternations of conditians of 

 greater or less intensity corresponding to established 

 astronomical cycles, and that the evidence of those were 

 to be seen in certain beds intercalated in the drift. He 

 admits, but explains away, the absence of evidence of the 

 regular recurrence of such effects throughout the previous 

 geological ages. 



The geographical theory which he principally combats 

 may be briefly summed up thus : There have been through 

 all time terrestrial m^vemants of wider or narrower 

 extent which have carried portions of the earth's surface 

 to depths below the lowest known abyss, and raised por- 

 tions through distances greater than the highest mountain 

 peak ; the depression and elevation of extensive areas 

 or ridges must, with sufficient precipitation, deflect 

 ocean currents and produce such snow.ields as would 

 feed the largest glaciers or ice-sheets required in ex 

 planation of the drifts, boulders, and accompanying phe- 

 nomena; there is evidence of movements on a grand 

 scale since the period of great cold and simil ir move- 

 ments have been going on up to a quite recent date, and 

 these, if extended over a longer time, would proluce all, 

 the effects required. 



In thecourseof these addresses our author is frequently, 

 led to speculate upon the causes and some of the effects 

 of earth-movements, and we find (^.jif. pp. 129, 267, 342^ 

 such a good case made out every now and then for the, 

 geographical theory that we cannot help feeling that the, 

 difference between the two schools is not irreconcileable, 

 but this is a vast question which cannot be settled tilli 

 many possibilities have been considered. 



The various theories referred to have been built i!pDn> 

 such a number of observations and hypothetical e.xplana- 

 tions that it is impossible to discuss them in one volumCj 

 of essays, still less in a short review of that volume. 



All the more, however, because the subject involves so 

 many matters of controversy, do we welcome the publica- 

 tion of the latest views of one who is so skilled an observer 

 as our author, and so competent to watch the progress ofj 

 research in regions beyond that which he has especially 

 studied. ■, 



WATER BACTERIA. 

 Diagnostik der Bakterien des Wassers. Von Dr. .Alex- 

 ander Lustig. Zweite sehr vermehrte Auflage. 128 pp. 

 (Jena : Gustav Fischer, 1893.) 



THIS is, we believe, the first attempt made to gather 

 together in a compact form the various descriptions 

 of bacteria which from time to time have been isolated 

 from water by different observers. In those cases where 

 the water investigator is concerned only with the number 

 of microbes present in any given water, the task of m^re 

 enumeration is such that, however anxious to do so, it is 

 almost impossible to take an intelligent interest in the 

 nature of the microbes present, beyond a superficial 

 glance at their more striking characteristics. But even 

 this is sufficient to indicate what numbers of different 



