12S 



KNOWLEDGE 



[June 1, 1899. 



that the acromion process lies on a level with the sternal 

 notch, but this is a mere compromise, and as such un- 

 satisfactory. Had we had the measurement from the tip 

 of the middle finger to the ground it would have been easy 

 enough to determine the position of the summit of the 

 shoulder and the level of the bi-acromial width. For lack 

 of satisfactory data the proportion of the head height is 

 omitted in three, and for like reasons it has been impossible 

 to determine the position of the knee, owing to the fact 

 that whilst the length of the limb from the summit of the 

 external malleolus to the articular plane of the knee has 

 been given, the distance of the malleolus from the sole of 

 the foot was omitted, and hence we were at a loss to 

 determine the height of the knee from the ground. Yet, 

 despite these deficiencies, most, we think, will admit that 

 they will learn much more from a hurried comparison of 

 the forms presented than from a prolonged and arduous 

 study of the tables of measurements presented by the 

 various authors. The long arms and the long legs of the 

 negro are at once apparent, the shortness of the upper in 

 contrast with the lower limb in the white man is very 

 evident, whilst the short trunk, and proportionately longer 

 lower limbs of the Australian are very strikingly displayed. 

 The proportion of the upper limbs in the Javanese and 

 Southern Chinamen is almost the same, but the shorter 

 lower limbs of the latter are readily recognised. 



It is along such lines as these that we venture to think 

 progress will be made. Provided we can obtain the 

 necessary measurements we can then present the results in 

 a form which will demonstrate with greater clearness and 

 more lasting effect those minor differences, on the sum of 

 which racial distinctions depend. 



SECRETS OF THE EARTH'S CRUST. 



By Grenville A. J. Cole, m.r.i.a., f.g.s., Professor of 

 Geology in the Royal Colleye of Science for Ireland. 



III.— THE MAKERS OF FLINT. 



THE association of flint with limestone, the former 

 material so hard, taking the mark of steel, and 

 the latter so soft and sectile, was observed by the 

 ancients, and even led to some confusion in their 

 nomenclature. ■ The contrast between the two 

 rocks was striking ; their relationship was certainly obscure. 

 Long before limestone was used as a building- stone or for 

 the production of lime, flints had been singled out for the 

 weapons of primitive man. At a later date, the cavernous 

 siliceous beds associated with certain limestones were used 

 for millstones, and were exported from one land to another. 

 When geology became a science, the mode of occurrence 

 of these rocks required explanation ; and difficulties were 

 at once forthcoming. The grand curving bands of nodular 

 flint, one beneath the other, on the headlands of the 

 English Chalk, form a veritable feature of the landscape, 

 and mark out the stratification of the series by their 

 horizontal, folded, or even vertical lines. The less known 

 flint-zones in the Portland beds of Dorsetshire play the 

 same part on the pale limestone face, where it is shajied 

 into cliffs against the sea. The darker colour of the 

 Carboniferous Limestone, however, often masks the flint 

 included in it ; but in this rock also, throughout England 

 and Ireland, siliceous bands are common. While there is 

 a greater tendency to the formation of continuous beds 

 rather than nodules, yet the Carboniferous flint often crosses 

 from one layer of the limestone to another, and forms 

 irregular lumps, quite in the Cretaceous style. 



* See the wise remarks of C.Tsalpinus, '■ De lletallicis" (1602), p. 84. 



By custom, rather than any accurate definition, flint 

 occurring outside the Cretaceous system has become 

 styled " chert," the homstein of the Germans. Some of 

 these cherts are duller than ordinary flint, owing to a 

 number of inclusions ; but this is by no means the rule. 

 Others, however, are merely sandstones cemented by 

 chalcedonic silica, like the brown bands in the " green - 

 sands " of Leith Hill. But all kinds alike represent an 

 alteration of the rock in which they occur — a feature that 

 was not present on its deposition from the waters of 

 the original sea or lake. 



We must bear lakes in mind, for many flint-beds, 

 crammed with fossils or casts of fossils, clearly originated 

 in fresh water. The Oligocene " Calcaire de la Brie," 

 well known in the wide plateau south of Paris, is often 

 converted into a scoriaceous flinty deposit, which has long 

 been found suitable for millstones. The fossils, Limnaa, 

 Plnnorbis. and the spherical oogonia of Cham, give no clue 

 to the cause of silicification, and are typical freshwater 

 forms. Long ago, however, Cuvierand Brongniart* showed 

 how the irregular hollows in such rocks resulted from the 

 removal of limestone in solution ; and they produced 

 artificial millstone-rocks, or meulieres, by treating siliceous 

 limestones with nitric acid. 



Macculloch,t about the same time, recognised the con- 

 nection of chert and limestone, and regarded chert as a 

 product of alteration. The views of D'Aubuisson des 

 Voisins* were still more lucid, when he attributed the 

 nodular masses of flint in the chalk to the coming together 

 of silica, which was once uniformly difl'used throughout 

 the mass. 



The origin of the silica, however, has given rise to many 

 speculations. The boUing springs, or geysers, of the present 

 day bring large quantities of silica to the surface in 

 solution. Wherever, again, we find lavas rich in silica — 

 notably the groups of the rhyolites and quartz-andesites — 

 their hollows tend to become filled with opal, chalcedony, 

 and agate ; and most of the precious opals come from 

 regions where volcanoes have been active in fairly recent 

 times. Sometimes the entire rock becomes silicitied ; that 

 is to say, its alkalies, alumina, lime, and magnesia, become 

 removed, and silica insidiously replaces them, the struc- 

 tures of the original rock being still retained. Even basalts 

 have thus been converted into jasper under the influence 

 of percolating waters, i 



Seeing that silica may be dissolved in spring-water 

 through the presence of carbonates of the alkalies, it is 

 natural to suggest that such water penetrates underground- 

 masses, and deposits chalcedony in their interstices. This, 

 indeed, seems the easiest way of making flint ; and even 

 irregular nodules can be explained as being formed 

 along the more conspicuous water-ways of the rock-mass. 

 Geologists of eminence, like M. Coquand,,, have not hesi- 

 tated to accept this view for ordinary flint. 



Certainly, when we find " tabular flint," as it is appro- 

 priately called, filling up irregular fissures, or coating the 

 planes of faults, we must admit that the material has been 

 deposited there from solution ; and the nodular flints 

 occurring in the same rock-mass seem but another phase of 

 the operation. But, even then, has the silica been derived 



* " Description Geologique des EnTii'ons de Paris " (1822), p. 41. 

 t "Geological Classification of Rocks" (1821), pp. 565 and 570. 

 t "Traite de Geognosie" (1819), Tome I., p. 318. 



§ C. Darwin, " Geographical Observations on Volcanic Islands" 

 (1844), p. 46. A similar case occurs in Angleser {Sri. Proc. if. 

 J)„hHn Soc, Vol. VII., p. 114). 



II " Traite des Koclies " (1857), p. 194. 



