May 27, 1892.] 



SCIENCE. 



305 



picking it up again, why should we regard it as an incredibly ex- 

 travagant assumption that a correspondingly large space is uncon- 

 sciously travelled over when we walk from one side to the other 

 of our granite block ? As the glimpse which we get of some of 

 the fixed stars is merely a ray of light which has taken many hun- 

 dred years to reach us, why should it be an altogether unreasona- 

 ble assumption that the light-ray from our granite block may take 

 a good deal longer to reach us than we are aware of ? As we 

 know, from experiments with birds, that there are sounds too 

 high-pitched for our ear to detect, is it not in every way natural 

 to expect that there are dimensions which the eye cannot de- 

 tect ? 



To sum up: As our inferences with regard to the material 

 world are rather the result of the limitations of our faculties than 

 limitations of so-called matter itself, are we not likely to get ahead 

 faster in the effort to broaden our concepts, and with them our 

 ability to form concepts, by modifying our inferences than by 

 trying to project our inferences into an unknown dimension? 



"W. P. Preble. 



New Tors, May 23. 



H. Carvill Lewis's Work on the Glacial Phenomena. 



The following communication from the wife of the late 

 Professor Lewis seems to me worthy of publication, both out 

 of respect to the writer and for the considerable amount of valu- 

 able information which it contains upon a subject that is now 

 uppermost in the minds of a considerable portion of the geological 

 world. I have no doubt that a large circle of your readers will 

 read it with great interest. G. F. Wright. 



OberllD, Ohio, May 23. 



Professor G. Frederick Wright, LL.B. 



Dear Sir : — YouE valuable reprint from the Journal of Science 

 for January, 1893, on "The Theory of an Inter-Glacial Submer- 

 gence in England " was duly received this morning, and after a 

 careful perusal of its contents I hasten to thank you for your cour- 

 tesy in sending it. 



The many questions relative to the causes and extent of the 

 great glacial epoch have, with its accompanying phenomena, oc- 

 cupied a large share of my thoughts during the past twelve years, 

 first, because of its surpassing interest and close connection with 

 the solution of some of the most important physical and astro- 

 nomical problems of the day; and, second, because I had the 

 pleasure of sharing all my husband's ideas and plans and much 

 of his field-work, from the day when he first made your ac- 

 quaintance at the Boston meeting of the American Association, 

 in August, 1880, to July 17, 1888, when, knowing the pre- 

 carious nature of the malady which had attacked him, he 

 gave all his unfinished manuscripts into my care, with the re- 

 quest, that, as I knew his inmost wishes in regard to them, 

 I would see that they were all completed and published as they 

 ought to be. The MS. for my husband's "Observations on the 

 Glacial Phenomena of Great Britain'' — so ably edited by the 

 Rev. Br. Crosskey of Birmingham, and covering 1,100 pages of 

 foolscap, has been in Washington since July last awaiting publi- 

 cation. Had it been printed before the paper which you have so 

 kindly sent me was written, I think you would have obtained a 

 slightly different impression of my husband's later views from that 

 expressed in the closing paragraphs. 



As the importance of clear definition in scientific work of all 

 kinds can hardly be overestimated, and as my husband's one wish 

 was to learn the truth irrespective of theories, which he regarded 

 merely as tentative hypotheses, to be thrown aside when they no 

 longer served the purpose for which they had been constructed, I 

 think that the term, ' ' Correction of some of Professor Lewis's earlier 

 working hypotheses,"' would give a clearer impression of the real 

 state of the case than the phrase, ' ' Correction of Professor Lewis's 

 personal equation," which to the world in general implies a con- 

 stant and known element of error in all that an observer sees or 

 does, and which must be strictly accounted for in the sum-total of 

 his work. 



As no one could be more anxious than I am (except my husband 

 himself) thatall errors of whatever sort shall be promptly eliminated 



from his life work, and as I have only too good reason for know- 

 ing the endless and varied misconceptions with regard to his views, 

 which have naturally arisen from the fragmentary reports of his 

 European observations that have hitherto been published, I think 

 that it may aid not only yourself but the scientific world gener- 

 ally if I send you a short synopsis of his later opinions. These 

 are briefiy as follows : — 



With regard to the terminal moraine in Pennsylvania, over the 

 last third of which he enjoyed the great pleasure and advantage 

 of your companionship, his opinion remained unchanged, that a 

 well-defined moraine had throughout the State defined the line of 

 the solid ice-front. 



The varying line of bowlders, scattered about as plums over a 

 pudding, found considerably south of the moraine at different 

 points in the western portion of the State, and which you both 

 decided to name " The Fringe," he at first suggested (see Report 

 Z) had been caused by a projection of the upper layers of ice — 

 which move more rapidly than those beneath them — over the 

 lower layers, which, as the ice rose hundreds of feet higher than 

 the moraine at its base, would naturally and in accordance with 

 its proper motion project the bowlders on the surface lying beyond 

 the moraine line. 



This view, however, was merely a tentative one, as he himself 

 confessed (see Report Z), and he abandoned it in 1886, as his in- 

 vestigation of the English glacial deposits drew toward a close. 



From many similar instances of "fringe" observed in Great 

 Britain, and also in Switzerland and northern Italy, he was thor- 

 oughly convinced that the phenomena in each case that he himself 

 examined had been caused by the damming back of streams flow- 

 ing toward the ice-front and forming bodies of water of varying 

 size and depth, which he called "extra- moraine lakes." 



Full details and diagrams relating to his studies of these will 

 be found in the forthcoming volume, and also his application of 

 them to the phenomena observed in western Pennsylvania, where 

 like features occur. The deposit of bowlders over the beds and 

 along the edges of these extra-moraine lakes he held to be largely 

 due to the drifting and melting of detached bergs, or cakes of ice, 

 from the foot of the glacier, in which the debris had been frozen, 

 or on whose surfaces the bowlders had been perched. 



I do not remember my husband at any time thinking that " the 

 fringe was the remnant of an earlier and distinct glacial period," 

 though in the Old World he found in many places very clear evi- 

 dence of there having beeu an advance or retreat, and a secoud 

 advance of the isolated or coalescing streams, which together 

 gave rise to the phenomena of the great glacial period. 



I do, however, recall his frequent statement that never in any 

 of his personal observations in America, Ireland, Great Britain, 

 Switzerland, or Italy had he found a single instance of a glacier, 

 ancient or modern, which had not at the time of its greatest ex- 

 tension been marked by a moraine at the foot of the sohd ice, 

 though these moraines often showed the greatest variety of form, 

 from a low, flat deposit of gravel, sand, or till, from a few feet to 

 a mile in width, and from a tiny ridge over which a man could 

 easily step to the gigantic drift hUls of northern Italy. 



Exceptions to these observations occurred in cases where the ice 

 moved from the land into the sea, as on the south side of the 

 Killarney ice-centre, on the west side of the Clare Mountains, and 

 in other instances, of which he himself has left a full description. 

 The moraine in some portions of western England was much dis- 

 turbed by the alternate elevation, depression, and re-elevation of 

 that section of the country during the period of maximum glacia- 

 tion, which caused a mingling and interbedding of morainic and 

 marine deposits. Special stress should here be laid upon my 

 husband's qualifying expression, "in my own experience," for he 

 never at any time denied that a glacier ever had existed, did now 

 exist, or could exist in the future without being bounded by a 

 terminal moraine; he simply said, " I, personally, have been un- 

 able to find one." 



With regard to your own admirable work in the State of Ohio, 

 and beyond it toward the Mississippi valley, where the ice-front 

 had not been marked by any definable moraine, — owing to its hav- 

 ing gradually lost momentum and become very much attenuated 

 in passing over a long, wide, and gently sloping plain till practi- 



