WCP2401

[1]¹

Harlton

Cambridge

5 Aug[ust] 1879

My dear Sir

I agree with all you say in your last letter. Mr Croll’s² remarks [1 word illeg.] the subject are substantially the same as yours but not nearly so full. But does not all you have said tend rather to show that geographical causes ^must have had more effect in producing changes of climates than astronomical ones?

Probably you have read the very odd paper supporting this view by Mr Campbell³ in the Q[uarterly]. J[ournal]. [of the] Geol[ogical]. Soc[iety]. for February last⁴. Hopkins⁵ propounded similar theories in the same journal in 1852⁶. This is a masterly paper and probably you know it. I think it would be well if you would suggest in Nature⁷ or in some other way that direct observations on the sun’s radiation at some station on the Equator would be valuable.

& I believe however that this particular theory is not has been shown to be untenable[.] [2] It seems as if the direct influence of the sun’s radiation in winter has but small effect in this country in winter. Our coldest weather often occurs with a clear sky & warmest with an overcast. Moreover the effect of the sun[’]s rays can only be proportional to the time he [sic] is above the horizon & indeed some way above it for save near the horizon his [sic] rays have little power. Hence although the change of the ^direct radiation of the sun is properly estimated as Mr Croll & you (&I) have done it yet the effect on the climate would not be so great as we have reckoned because during the time he [sic] was below the horizon (the greater part of the 24 hours) it would make no difference whether he [sic] was near or far off except so far as he [sic] had heated the air and earth during the day. I feel to be a sort of Advocatus Diaboli⁸ in thus picking holes in Croll[’]s great theory but I confess the more I think about [3]⁹ it the more I feel it is still only a theory though a very grand one.

Touching ice caps — I think there is sufficient geological evidence to support such an extension of the ice as Mr Croll has shown in his plate V. T_s at of course the a polar ice cap is a different thing. Adhémar¹⁰ was the first I believe to suggest their existence and the consequent raising of the ocean level alternately at each pole by attraction.

But the whole question is so intricate that one hardly knows what to think about it. The question now disputed between first rate geologists as to whether the boulder clays of England (not of Scotland) are terrestrial or marine is intimately involved. I myself believe them to be marine. I have found a stone pierced by boring shells in the boulder clay here and also rolled gryphons[?] with [1 word illeg.] perforations in gravel derived from the B[oulder] Cl[ay]. Again the great submergences on the western side of this country do not appear to have been matched by others on this side & to [4] be equally explicable by unequal [1 word illeg.] & [1 word illeg.] of the land, so that in my opinion the extent of the submergence has been exaggerated.¹¹

I am very hard of belief too about the warm climates of the pole being explicable by on the Crollian hypothesis. The remains you speak of at page 244¹² might be so: but where one comes to the so called Miocene¹³ deposits, and considers that probably they required a correlative world of living creatures to fertilize the seeds & so forth, and that one or two clear sights intervals during the six months’ win sunless winter might probably have reduced the temperature sufficiently to kill many of the species, it is hard to believe they could have flourished there so long. With ourselves we know for how many years certain plants will thrive, while one of frost will destroy the growth of years; as happened in 1860, when I saw [1 word illeg. struck through] many oaks which had been killed in one night. It seems to me that the artificial preservation of tropical plants in darkness is a very different thing from their spontaneous choice of a habitat involving such a condition.

[5]¹⁴

Indications of glacial & mild climates throughout geological time.

There is a paper (of course you know it) by Prof[esso]^r Nordenskiöl[d]¹⁵ in the Geol[ogical]. Mag[azine]. Decade II vol[ume] II¹⁶ in which he combats the idea of recurring periods at the north pole of warmth & cold in the polar regions. I think myself that if the boulder clay is marine (some of it at any rate) we ought to find ^{former beds of} it interstratified with other rocks. But Prof[esso]^r N[ordenskiöld]. denies there being anything of the kind in polar regions. & Now we are told of a glacial deposit in an old rocks of unknown age (the [1 word illeg.] group) somewhere near [1 word illeg.] about lat[itude] 20° can mean astronomical or geographical causes account for such seemingly contradicting facts (if they be facts)? as glacial deposits of early times near the equator & now near the pole[.]¹⁷ Must we not have a geographical shift of the pole? Haughton¹⁸ made a great blunder in attributing the former warm climates of the pole to residual earth[?] heat. May he not also be wrong in his "rat in [1 word illeg.]" argument? [6] If you put back the Miocene epoch 850,000 years this is nearly a tenth of the 100 million years which Sir W[illiam]. Thomson¹⁹ allows for the whole duration of geological time. Without allowing the ^full force of his arguments it went at any rate too far back for the Miocene period[.]

If I recollect rightly Prof[esso]^r Duncan²⁰ has shown that species of coral on the two sides of the isthmus of Panama are the same, pointing to a somewhat late formation of the dividing ridge. What a great change that would make in the system of currents! Would its ^absence not at once bring glacial conditions down upon the northern points of this Island and on Scandinavia? If our boulder clays are marine there must have existed with existed at the time of their deposit a northern current instead of the present Gulph [sic] stream in order to [7]²¹ bring the northern rocks over our southern lands. These considerations point [to] a geographical rather than to astronomical cauus[e].

This letter is a sad rigmarole. But what I want to express is that the Crollian hypothesis is not the totus teres atque rotundus²² theory which it appears at first sight to be.

You mention having seen some statement of Sir J. Herschall’s²³ [sic] that the direct maximum sunheat at the Cape is greater than that in equal north latitude. I see that he makes a remark to the same effect about the sun’s power in Australia. A. S. [1 word illeg.] 7^th Ed[itio]n [1 word illeg.] 369.

Believe me | truly yours | Osmond Fisher [signature]