NA TURE 



[November 9, 1893 



by some high authorities, including himself, Mr. Darwin, and 

 Air. James Geikie. While we may all share in this congratula- 

 tion, it must be remembered what it involves. 



It has been the fashion with an extreme and aggressive school 

 of glacialists to postulate an excavating tendency in ice to which 

 the formation of lake basins and valleys-without-outlets in 

 mountain districts has been attributed. They will not allow 

 that rock basins are due to any other cause than "omnipotent 

 ice." They scoft' at explorers of the mechanics of ice in Alpine 

 countries, like Prof. Bonney and Mr. E. Hill. They jeer at those 

 who have devoted much patience to unravelling the mysteries 

 of Plutonic action, like Prof. Judd and others, who attribute a 

 large number of lakes to dislocations and to foldings of the sub- 

 jacent rocks. It is no use, in arguing with them, to refer to 

 mechanical difiiculties like those involved in conveying thrust 

 of more than a certain amount through a substance like ice, 

 which is known to crush under a moderate pressure, nor to pro- 

 duce any number of mechanical arguments against the capacity 

 of ice to erode lake basins such as those in question ; nor is it 

 any use appealing to the stupendous geological difficulties 

 against their conclusions which have been accumulated by quite 

 a number of skilled geologists at home and abroad. All these 

 •efforts are futile, for we are told that the ice to which appeals 

 must be made is quite a different thing to any ice we can ex- 

 periment upon or examine, and that it must not therefore be 

 measured by the ordinary laws that govern ice such as we know it, 

 and this appeal to transcendental ice is considered to be orthodox 

 science in the nineteenth century, an age when induction is 

 supposed to have become a supreme law to us all, and when 

 rt/rzwi postulates are generally discarded from the realm of 

 physical research. Let this pass, however, and let us test the 

 •question in another way. Let us test it, in fact, by this very 

 case of Brazil, 



There has never been a glacial period in, nor are there 

 traces of glacial action in the highlands of, Brazil, we are told 

 by Dr. Wallace. Granted. How then can Dr. Wallace, ar.d 

 those who agree with him in this matter, explain the existence 

 on the plateau of Bahia of perhaps the largest and most remark- 

 able collection of rock basins in the world, rock basins exist- 

 ing, too, in close juxtaposition with most i^erfect examples of 

 giants' cauldrons on the largest scale. This is assuredly a 

 dilemma for the transcendental school of geologists. 



Let me quote from Mr. Allen's graphic descriptions of these 

 rock basins. Speaking of the plateau of Bahia, he says : "Over 

 this whole region there is an almost entire absence of loose 

 materials on the surface . . . slight knolls and shallow basins 

 alternate which rarely difter more than 20 or 30 feet in eleva- 

 tion, fn the rainy season many of these basins become filled 

 with water, forming shallow lagoas varying in area from less 

 than one to more than 50 acres, from most of which the water 

 evaporates in the dry .--eason .... So numerous were these 

 lagoas for more than 50 miles that it seemed natural to speak 

 of this region in my notes as the "Lake Plain." Almost 

 everywhere the elevations are evenly rounded, indicating that 

 the rocky crust has been exposed to rain and probably long 

 continued abrasion. But the absence of abraded materials 

 seemed most remarkable ; very rarely were even loose boulders 

 observed, though a few such were repeatedly noticed. At fre- 

 quent intervals there were irregular holes in the rocks, usually 

 nearly filled with water, to which the inhabitants give the 

 name of 'caldeiraos.' These caldeiraos are of frequent occur- 

 rence Nearly all of the considerable number examined 



proved to be genuine pot-holes, and some of them were of great 

 size. The largest one I measured was elliptical in outline, 18 

 feet long, 9 or 10 in width, and 27 deep, with smoothly worn 

 sides. . . . These pot-holes often occur out on the plain, far 

 away from any high land, and they are sometimes found exca- 

 vated on the summits of slight bulgings in the plain, or even on 

 the top of a hill." 



I would ask, in all seriousness, whether, if phenomena like 

 these had been described from the Alps or from Nova Scotia, 

 they would not assuredly have been pointed to by extreme 

 glacialists as the unerring footprints of great ice-sheets, and 

 yet Dr. Wallace, who is a champion of the school, repudiates 

 the former glaciation of Brazil altogether. 



What is to be said in regard to this dilemma then ? It is 

 quite clear that either the facts must be disputed (and who is to 

 dispute them ?), or else the champions of ice at-all-hazards must 

 concede that rock basins and giants' cauldrons can be made by 

 other agencies than ice. If so, they can be made as well in one 



place as in another. If they could be made by other causes on 

 the plateau of Bahia, vvhy not in the highlands of Tasmania? 



I am bound to say I was taken aback by Dr. Wallace's com- 

 ments on a letterfrom one of your correspondents, whichappeared 

 in Nature a short time ago. That gentleman professed to make 

 an exploration of certain parts of Tasmania with another ex- 

 perienced geologist. They were both champions of the glacial 

 theory. They both went prepared to find traces of glacial action 

 there, and certainly in our latitudes no evidence seems more 

 easily discriminated, and they came back convinced that in the 

 districts where the rock basins of Tasmania abound, there are no 

 traces of glacial action to be seen. They could find none. 

 Mr. Johnstone, who has written an elaborate and detailed 

 geological memoir on the island, and who has explored it in 

 many directions, could find none either, save on the western 

 flanks and in the valleys of the Tasmanian Alps in the western 

 part of the island, where it has been long known that traces of 

 former local glaciers exist. There is absolute unanimity among 

 the native geologists that nothing in the shape of ice-sheets 

 existed there, and there is no ice-spoor in the central districts 

 where the great Tasmanian lakes occur. Dr. Wallace's 

 answer to all this was certainly unexpected. He has not 

 himself visited the island, and yet he disputed not only the 

 inferences but the facts and the observations. Why should the 

 voice of Esau be listened to and approved in Brazil, and that of 

 Jacob be repudiated in Tasmania ? Mr. Johnstone and the 

 other observers in Tasmania are assuredly to be trusted in 

 such an issue quite as much as Prof. Branner. I cannot see on 

 what ground the discrimination is made, except the desperate 

 inconvenience of postulating a glacial nightmare in the tropics. 



Assuredly the whole difficulty lies in championing a theory of 

 the origin of lakes, unknown in geology until introduced by 

 Ramsay, whose extravagance at times may be measured by some 

 of his phrases addressed to the British Association when he pre- 

 sided over the geological section. From all sides there comes a 

 revolt against this theory, which is based on no empirical evi- 

 dence, and is at issue with the mechanical properties of ice so 

 far as we know them, and with the observations of practised 

 observers of the first rank. I am bound to say that those 

 geologists who habitually make appeals to forces in Nature, 

 and to properties of matter which are purely hypothetical and 

 unwarranted by experience, are leading us back to times when 

 Aristotle and deductive reasoning dominated European thought, 

 and when Bacon had not yet taught us better things. 



My attention has been called to an oversight in my previous 

 letter. Among those who many years ago did good work in 

 dissipating the particular glacial monster that was generated in 

 the valley of the Amazons, was my old friend Dr. Woodward, 

 whose papers on the subject in the volume of the Anit. and 

 Mag. of Nat. Hist, for 1871, pp. 59 and loi, I had overlooked. 



IlEMiY H. HOWORTH. 



30 CoUingham Place, Cromwell Road, October 27. 



Correlation of Solar and Magnetic Phenomena. 



I WAS glad to see (Nature, vol. xlix. p. 2) in the notice of 

 Miss Gierke's "Popular History of Astronomy," that at- 

 tention was drawn (l) to the correspondence in time between a 

 certain luminous outburst seen on the sun on September i, 1859, 

 by Carrington and Hodgson, and a disturbance of the magnets 

 at the Kew Observatory : and (2) to the statement of the late Mr. 

 Whipple that the magnetic movement was really a small one, 

 and that in his opinion the observed correspondence was a mere 

 accidental coincidence. Those who have read Carrington's 

 original account (Monthly Notices of the Royal Astronomical 

 Society, vol. xx. p. 13) will remember that at the time he him- 

 self did not lean towards hastily connecting the phenomena, 

 remarking that " one swallow does not make a summer." But 

 authors of text-books on astronomy, who may be only to a 

 partial extent observers, are too apt to state the matter in such 

 a way as to give an impression that we have here an undoubted 

 instance of direct connection, instead of a case of apparent con- 

 nection, to be taken merely for what it is worth, seeing that the 

 occurrence has remained to the present time without corrobora- 

 tion. I should like to take the opportunity to support, in the 

 fullest manner, the opinion of Mr. Whipple, which acquain- 

 tance with the Greenwich magnetic registers tells me to be a 

 true one. The magnetic movement in question, as recorded at 

 Greenwich, was similarly small. 



But the erroneous impression lives long. May I therefore be 



NO. 



T254. VOL. 49] 



