5J52 



NATURE 



[April i8, 1895 



The following figures represent the most striking phases, as 

 nearly as may be at intervals of five minutes. 



Fig. I shows how the streak extended from the cometary 

 head so as to form a long wavy tail, and represents also the 

 streak at its greatest length. As indicated in the sketch, there 

 was a central portion much more brilliant than the rest, running 

 from the head into the body of the streak. 



In Fig. 2 the streak is seen when it had more the appearance 

 of a rainbow than of a comet ; and it was verv noticeable that 

 one side — that towards the north — was much brighter than the 

 other. 



Fig. 3 shows how the "head" began to shrivel up — shorten- 

 ing the streak. The glimmering appearance of the "shrivel- 

 ling " put me very much in mind of the motion of the air over 

 a "hot heap" (of slag); the tail end began to broaden out 

 somewhat. 



In Fig. 4 the streak has taken a very pronounced arrow- 

 headed .shape, and, as if to complete the resemblance, the 



North. 



Fig. I. 



Fic. 2. 



Fic. 



Fig. 4. 



South. 



Fic; 



shimmering part look the form of the feathering ; whereas in 

 the preceding figure it had more the appearance of combteelh. 

 The more brilliant parts are indicated hy daiker shading. 



In Fig. s the streak has consideiaMy shortened and 

 broadened out in the west, where it soon alterwauls mingled 

 with faint auroral rays which had come round from the northern 

 horizon. 



I may lay, in general, that the appearance; were singularly 



and hrillianl. The sky was very clear at the time, 



■ ;ar wa.s visible through the most brilliant parts of 



- Inuring the time the streak was visililc there was a 



(aint rii-play of aurora on the northern horizon, which, as I 

 have already said, worked round lo the west and cau>;hi the 

 la»t of the streak. Jas. G, Richmond. 



Muirkirk, N.B. 



NO. 1329, VOL. 51] 



THE AGE OF THE EARTHS 



TLL-HEALTH has hitherto prevented my making the 

 ^ comments which seemed called for by Lord Kelvin's 

 friendly article of March 7, in reply to my communi- 

 cation of January 3. Perhaps I may be allowed not 

 merely to restrict my remarks to this article, but to 

 deal more generally with the subject, in the hope of 

 clearing away the misapprehensions which exist between 

 modern geologists and palxontologists, who are no 

 longer uniformitarians, and physicists who are repre- 

 sented by Lord Kelvin. 



The arguments as to the age of life on the earth are 

 based on considerations of (i) geology and paleontology ; 

 (2) tidal retardation and shape of the earth ; (3) the 

 cooling of the earth from an initially hot condition ; 

 (4) the age of the sun. 



(i) From geology. The leading geologists declare 

 that the great thickness of sedimentary rocks created 

 since the Lower Cambrian, which are almost the oldest 

 fossiliferous rocks, can only have been produced during 

 iTiany millions of years. 



It is difficult to get geologists to give even wide 

 limits for the age of the Lower Cambrian.-' Their calcu- 

 lations are based not upon the rate of accumulation 

 of sediment in one of our quiet oceans, but upon 

 the rate of degradation in valleys where the rate is 

 greatest at the present time. They make this declara- 

 tion, thinking that for thclast thirty three years it has been 

 authoritativelydeclaredby physicists that such anestimate 

 is absurdly great. I have no doubt that they have done 

 their best to keep this estimate as. low as possible, for 

 they have a great interest in making geological theory 

 agree with physics. Some physicists tell them that the 

 flaw in the geologists' reasoning consists in their not 

 taking into account the much greater tidal actions of 

 the past. When tides rose and fell many hundreds of 

 feet, and swept over tens or hundreds of miles of fore- 

 shore, there must undoubtedly have been a more 

 rapid formation of sedimentary rock than anything of 

 which we now have experience. The geologists' answer 

 is : — We acknowledge th \t all nature's actions were 

 on the whole, possibly, more intense in the past. We 

 know from Prof. Darwin's development of Prof. Purser's 

 theory that the moon was undoubtedly nearer the earth 

 in palaeozoic times, and the tide influence was there- 

 fore greater. But there seems to be no method of 

 even approximately calculating how much greater the 

 tidal influence was. Whilst one great astronomical 

 authority speaks of tides of 500 feet deep in pala;ozoic 

 times, Prof. Darwin himself thinks that two or three 

 times as great as at present may be an excessive estimate. 

 There is a good deal of geological evidence for much 

 smaller seas than at present, and even if tidal influence 

 were greater the actual tides may have been much 

 smaller than now. Of positive evidence in our favour, 

 we have the fact that numerous examples exist of 

 palaeozoic locks which are identical in almost every 

 physical way with tertiary rocks, and it is difticult 

 to believe that they can have been deposited under 

 very different conditions. Again, nearly all the old 

 sedimentary rocks were laid down near coasts where 

 tidal action would be inost violent. Yet even low 

 down in the Cambrian we find the remains of creatures 



' I n this paper free uuc has been m.idc of many suKKC^'tions from Prof. 

 Filrg'-mld, 



" I'hcir data arc i.f this nature • — Of fossiliferous rocks successively 

 formed the !• tal thickness may be laken as not less than 80,000 feet. Over 

 Ihc areas of the t);uiii . ilrained by many rivers ihe rati- of deniidatinn is 

 kno ' n witli -uffi. ienl accuracy for apprdxiniatetalciilaiioii. ofthcl)asio 

 of the Mississippi a thickncs> of one foot of rock i^ reinuved in 6000 years : 

 Ihr Ganges, 3J58; the Ho.inK Ho. 1464 ; the Rhojic. 1518; the Danube, 

 CB^O; the I'o, 7^9: ihe Nilh, 4733 (Sr A. Geikie, (.Jc-ol. .-oc. of Gla-gow. 

 18(8). I have heard that I'rol. .Sollas dcmaod> Ic-s time th.an other 

 grolo^isis : t^ut since tt-is paper was written, I have setn (Nai URE, April 4) 

 that even he does not care 10 put the age of the Lower Cambrian at inncb 

 less than 17 million years. 



