46 



KNOWLEDGE 



[Makch 1, 1898. 



would practically mark the boundary between terrigenous 

 and pelagic deposits. Very large and swift muddy rivers, 

 like the Congo and the Amazon, however, cause the 

 former to travel to even greater distances. The work 

 of icebergs makes another exception to this rule ; for 

 they drop stones and mud all along the path of the ocean 

 currents which di'ift them into warm seas, thus tending to 

 some extent to confuse the limits of terrigenous and pelagic 

 deposits. Winds also blow desert sand and fine volcanic 

 ashes for hundreds of miles out to sea. Still, the broad 

 distinction remains. 



Before passing on to consider somewhat in detail the 

 nature and origin of some of the deposits mentioned in the 

 above scheme, let us look for a moment at thair geographical 

 distribution, as well as the depths at which they occur. It 

 is estimated that terrigenous deposits cover one-fifth of the 

 area of the oceans (or one-seventh of the earth's surface) ; 

 so that the pelagic deposits occupy four-fifths of the ocean 

 bed (or fom'-sevenths of the earth's surface — the land 

 occupying two-sevenths). 



Charts I. and II. have been reduced by photography from 

 two larger drawings made by the author. No. I. is a 

 generalized form of the map in the report of Murray and 

 Eenard, and No. II. is based on a map by J. Bartholomew. 

 The first shows at a glance the distribution of the principal 

 marine deposits, the second shows the depth of the ocean, 

 as far as known at present ; and it is instructive to 

 compare the two charts in order to see how far depth is a 

 factor in determining the character of the deposits lying 

 on the sea floor. It will be apparent at once that, broadly 

 speaking, depth is the chief factor, although other causes 

 (such as latitude and temperature) have their influence. 

 Take, for example, the distribution of the globigerina ooze* 

 (shown by vertical lines) and you will see how it occupies 

 the shallower parts of the Atlantic Ocean between 1000 and 

 2000 fathoms and between 2000 and .3000 fathoms, and 

 parts of the Pacific and Southern Oceans between 1000 and 

 2000 fathoms. As we shall see in the nest paper, it is most 

 typically developed at depths between 2000 and 3000 

 fathoms, but its average depth is just about 2000 fathoms. 

 Over part of the great Southern Ocean its place is taken by 

 diatom ooze. Still, even that ooze will contain a very fair 

 proportion of foraminifera. Look again at the large area 

 surrounding the east of Australia and the many groups of 

 islands to the north and east, and you will see this same 

 ooze, &c., occupying most of this region within the depth 

 range of 1000 to 2000 fathoms. 



But the red clay brings out the importance of depth as 

 a factor in this matter of distribution much more plainly. 

 Take the Atlantic Ocean, and you will find four large 

 patches of this deposit, lying in four or more hollows 

 where the depth (shown by cross lines) is 3000 to 4000 

 fathoms — two on each side of the well-known ridge that 

 runs straight down the Atlantic. Taking the Pacific, we 

 find red clay in a depression off the south-west coast of 

 South America, with globigerina ooze surrounding it 

 where the depth is less. The greater part of the Pacific 

 we see has red clay, the globigerina ooze confining itself 

 to the shallower waters (1000 to 2000 fathoms) nearer 

 land, or gi-oups of islands. The long and rather wide 

 strip of diatom ooze in the southern hemisphere is 

 peculiar, and its presence there must be explained by other 

 causes. So with the two patches of radiolarian ooze — 

 one in the Indian Ocean, and the other in the centre of 

 the Pacific (marked in Chart I. by little marks like a V). The 

 dotted spaces mark coral mud, derived from the wear and 

 tear of coral reefs, and their positions can easily be 



• See Knowledge, Vol. xv., p. 164. 



accounted for ; but even these are partly limited by depth. 

 The three little plain spaces on the ridge of the South 

 Atlantic denote pteropod ooze, and there is another one 

 between New Zealand and the Equator. 



The areas around the continents and islands in which 

 terrigenous deposits are being laid down is marked in 

 Chart I. by a plain white area, and it need hardly be 

 pointed out that depth is the chief factor in determining 

 the areas over which they spread. 



But it must not be supposed that the boundaries of the 

 various deposits are as accurately known as might be 

 implied by the definite bounding lines shown in Chart I. 

 In reality, these deposits shade off one into the other in a 

 gradual manner, such as should be indicated by shading 

 rather than by sharp lines. It is necessary also to add 

 that some of these bounding lines are more or less 

 hypothetical in places, and have been got by filling in 

 outlines suggested by mapping down the results of sotmding 

 and dredging operations. So with regard to the ocean 

 contours ; they are not yet fully mapped out, as our know- 

 ledge of certain areas is limited. If future soundings 

 modify some of the contour lines shown in Chart II., it is 

 pretty certain that changes on the other Chart will be 

 required ; for, as we have shown above, depth is the chief 

 factor in determining the distribution of deep sea deposits. 



ON CERTAIN LOW-LYING METEORS. 



By Charles Tomlinson, P.R.S., F.C.S., &c. 

 1. — The Ignis Fatuus. 



THE term "low-lying meteors " involves something 

 like a contradiction, since the word "meteor" 

 (p. crtctf/jo?, " high ") originally referred to appearances 

 in the upper regions of the atmosphere, such as 

 the Auriira Boiralis. As science advanced, the 

 word was extended to all the varied phenomena that are 

 connected with the weather and embodied in the term 

 " meteorology." Our present purpose, however, is to give 

 some details on a subject that seems to have fallen into 

 hopeless confusion — namely, the phenomena to which the 

 term iipu's fatui has been applied by the English, feu.r 

 foUets by the French, and In-lU-htcr by the Germans. 



Some old XDupils of mine were seeking for information 

 on the subject of the Kjnis futum, or " will-o'-the wisp," 

 also known as " jack-o'-lantern," and turned to one of 

 those popular books grandly styled "Guides to Knowledge," 

 and read as follows : — 



*' This luminous iippearaiiee (which haunts meadows, bogs, and 

 marshes) arises from gas of putrefying animal and vegetable sub- 

 stances, especially from decaying fish. These luminous phantoms are 

 so seldom seen because jihosphoric hj'drogen is so very volatile that it 

 generally escapes into the air in a thinly diffused state. They fly 

 from UB when we run to meet it, because we produce a current of air 

 in front of ourselves (when we run towards the i(jnis fatuus) which 

 drives the light gas forwards. It runs after us when we flee from it, 

 because we produce a current of air in the way we run, which attracts 

 the light gas in the same course, drawing it after us as we nm away 

 from it. The Welsh "corpse candles" are the same thing as the 

 ignis fatuus. Swarms of luminous insects passing over a meadow 

 sometimes produce an appearance similar to the ignis fatuus." 



This passage contains nearly as many blunders as lines. 

 The ignis fatuus is not seen in meadows ; it is not due to 

 putrefying animal matter ; there is no such gas as 

 phosphoric hydrogen — the gas really meant is one of a 

 series of inflammable compounds, in naming which the 

 Latin word un-t ("it will burn ") is introduced, such as 

 phosphuretted hydrogen, carburetted hydrogen, &c., but now 

 known by the shorter terms "phosphide," "carbide," &c. 

 As a specimen of English composition may be noted the 



