June 1, 1892.] 



KNOWLEDGE. 



103 



shore in the south-west, together with the evidence of the 

 near neighbourhood of a coast afforded by the sandstones 

 of Saxony and Bohemia, indicates that this sea was a 

 III,,,-,' riausum (in a geographical, not a political sense) 

 somewhat Uke the Mediterranean or the Black Sea. Now, 

 from the apparent similarity of Chalk to the ooze formiur^ 

 HI the abyssal depths of the Atlantic and the other lar^e 

 ocean basins, it was taught but a few years ago that the 

 Chalk itself was deposited in an ocean of similar depth. 

 The mnre claii.sum theory, ho\rever, is of itself a sufficient 

 obstacle to the acceptance of such a view, since it is im- 

 possible to conceive that a sea of such small dimensions 

 could ever have had depths at all approaching those of the 

 Atlantic. The Atlantic theory, if we may so call it, qf the 

 Chalk was, however, at once and for ever dissipated bv 

 the researches carried on during the voya"-e of the 

 "Challenger." Those researches showed that the so- 

 called abyssal deposits, instead of being verv like the Chalk 

 were really very different. Even the ooze has not the 

 purity of the Chalk ; while the large areas of red clavs 

 covering the ocean basins have no analogy in the latte"r 

 Moreover, it has been proved that the abyssal deposits are 

 laid down at a rate of almost inconceivable slowness— so 

 slowly indeed that even meteoric dust forms an appreciable 

 portion of the red clays ; while the ear bones of whales ' 

 and teeth of sharks that strew the ocean floor have lain 

 there so long as to have become coated over with a thick 

 layer of manganese precipitated from the water of the 

 ocean. On the other hand, the remains of fishes and 

 other delicate organisms which occur so beautifullv pre- 

 ser^-ed m the white Chalk clearly indicate that its 

 deposition must have been comparatively rapid, and must 

 have taken place m a sea where there was abundance of I 

 mineral matter either m suspension or solution. A^ain 

 the fauna of the Chalk, especially the sponges, is°one 

 such as would be found in comparatively shallow seas 

 and IS quite unlike that of the Atlantic depths. In- 

 deed, It is quite probable that the Chalk sea may not 

 have exceeded some one to two thousand feet in depth. 

 The great difficulty in regard to the Chalk is, indeed, to 

 explain Its purity, and the very rare occurrence of drifted 

 materials found embedded in it. The man- clamum, with 

 no tides and perhaps but few large rivers flowing into it 

 and Its shores largely composed of hard crvstalline rocks 

 hke those of Scandinavia and the Ardennes,'will, however 

 to a certain extent remove this difficulty. Even then' 

 however, it is doitbtful how sufficient material for the 

 formation of the Chalk could have been obtained ; and 

 aceorchngly one of our most eminent Uvin<^ .-eolo^ists 

 suggests that, m addition to its partially organic origin, 

 Chalk may have been largely formed by a chemical pre- 

 cipitate of carbonate of lime. 



Be this as it may, the degradation of Chalk from its 

 former position as a supposed typical abvssal deposit has 

 taught the great lesson that almost all the stratified rocks 

 with which we are acquainted were laid down in com- 

 paratively shallow water, and consequentlv has led to the 

 general acceptance of the gi-and doctrine of 'the permanence 

 ot continents and ocean basins. By this, of course, it is 

 not meant that the whole areas of several of our continents 

 such as Europe, have not been (as we know thev have) 

 many times over, beneath the sea. Indeed, what "we haw 

 ah-eady said as to the extent of what we mav call the 

 cretaceous Mediterranean, shows that at a comparatively 

 late period of geological history a large part of central 

 iMirope was sea. Neither does this doctrine forbid such 

 changes m the present configuration of the earth as would 

 be implied by a land connection between Africa and 

 southern India. What, however, it does say, and that in 



the most emphatic manner, is that where continents now 

 are there deposits have always been going on, and there 

 land, ot larger or smaller extent and of ever varyin<^ con- 

 tour, has always been ; while the great ocean basins, like 

 those of the Atlantic and Pacific, have existed as such 

 since the globe emerged from its primeval chaos. This 



ChTlk-r ^^'^"'"^ "''^''^ ^''''°" '"""^^^ ^^' "" '"'""l' °^ 



_ \\e have, however, by no means vet exhausted the 

 interest connected with the subject of Chalk. In the first 

 p ace the gradually increasing marly character of the lower 

 Chalk points to a condition when the sea was much less 

 deep than at the period of the white Chalk. If indeed 

 w-e go lower down m the rock series, we shall find the white 

 character of the Chalk has completely disappeared when 

 we reach the underlying blue '• gault " of Folkestone, which 

 implies the existence of currents or rivers largely charged 

 with mud. Still further back, wo have the freshwater clavs 

 and sandstones of the Weald of Kent and Sussex • and 

 we thus learn that at that period southern England was in 

 j the condition of a large delta, after which there was a 

 ; gradual subsidence, culminating in the w,i,r damum of +hc 

 period ot the white Chalk. Then, agahi, we have seen 

 ; tow tlie •' architectural style - of a rock, as exemplified bv 

 its tossils, IS the one all important point connected with 

 It ; and the alteration of the English Chalk into the 

 cretaceous sandstones of Saxony ought to have prepared 

 us lor more extensive modifications of these rocks as we 

 proceed to regions still more remote from where they are 

 typically developed. If, then, we turn to a geological map 

 of Europe, we shall find a large area of its southern half 

 coloured m, as being formed of cretaceous rocks— that is 

 rocks equivalent m point of age to the white Chalk The' 

 description, or stfll better, an actual examination of these 

 rocks will show, however, that thev have but little in 

 common with the white Chalk. They consist,indeed,of hard 

 compact, and often dai-k-coloured limestones, containing, 

 many fossils identical with those of our own Chalk together 

 with certain others of difterent types ; thus showing that we 

 have entered an area where the conditions of life were some- 

 what diflerent from those obtaining in the mare clau.sum of 

 the white Chalk. From the centre and south of France these 

 cretaceous limestones may be traced across the Pyrenees 

 into Spain, and so into North Africa, while eastwards thev 

 extend across the Alps into Switzerland, Italy, Bul-^aria 

 Koumania, and thence along the Mediterranean basin into' 

 Asia, ihat these rocks stretch far into the heart of \sia 

 IS now well k^o«^l, and since rocks of somewhat similar 

 type contaiumg well-known European cretaceous fossils 

 are tound in the inner Himalayas, it seems highly probable 

 tliat this southern cretaceous sea connected the Mediter 

 ranean with the Bay of Bengal. Whereas similar 

 cretaceous fossils occur on the east coast of India in the 

 neighbourhood of Madras, and since there are some very 

 remarkable similarities between the freshwater rocks of the 

 peninsula of India and those of South Africa, while many 

 animals are now common to those two countries, there are 

 very strong reasons for considering that peninsular India 

 (which was then cut off from the rest of Asia by the 

 cretaceous sea) had a laud connection with the Cape by 

 way of Madagascar. We know indeed that this southern 

 cretaceous sea communicated freely with the Atlantic by 

 what is now Spaua and France, and we are thus led to 

 conclude that there was formerly a direct sea communication 

 between the Atlantic and the Bay of Bengal by way of 

 central Asia. Europe and Asia then formtd a northern 

 continent separated by this cretaceous sea (of which the 

 Mediterranean is the shrunken remnant) from a southern 

 contiuent which included both Africa and India proper 



