260 



KNOWLEDGE. 



[November 1, 1894. 



thirty minutes the impurity at nine feet fi-om the iioor was 

 very great, the colour being an intensely deep blue. 



The wide range of the indications of the instrument, 

 from pure white to nearly black-blue, makes the estimate 

 of the impurity very easily taken with it, and as there are 

 few parts to get out of order, it is hoped it may come into 

 general use for sanitary work. Mr. Aitken was quite 

 enchanted with the beautiful colours in his preliminary 

 experiments, but he is even more pleased at the practical 

 benefit which the koniscope may effect when thoroughly 

 adjusted and intelligently used. 



THE CLIMATE OF THE CAMBRIAN PERIOD. 



By Prof. J. Logan Lobley, F.G.S., &c. 



THERE is a widely spread impression that the state 

 of the surface of the earth and the prevailing 

 chmatal and atmospheric conditions of pre- 

 Quaternary geological periods were quite unlike 

 those that now exist, so much so indeed as to be 

 altogether unfitted for the human occupation of the planet. 



The vast number of extinct organic forms revealed by 

 palffiontological investigation, and the great divergence of 

 many from those now living, as well as the late coming in 

 of new species, have largely contributed to produce this 

 behef ; but, perhaps, it has been most encouraged by the 

 fact of the vegetable origin of coal, since it has been 

 thought necessary by some writers to assume such atmo- 

 spheric and climatal conditions for the production of the 

 Carboniferous flora as would be quite inimical to the 

 existence of man. And yet the records of the rocks 

 conclusively establish the great fact, that not only in 

 Tertiary and Secondary times, but also in Palseozoic 

 times— indeed. La the earhest Palseozoic times — general 

 inorganic conditions were very similar to those of to-day. 



As has been said by a recent writer on fossils, when 

 referring to distant geological periods, " Flesh and blood 

 were then what they are now, and fulfilled the same func- 

 tions. Bones grew then as they grow nowadays. To 

 those bones were attached muscles, which expanded and 

 contracted just as muscles do now. Wings were used for 

 flying, fins and paddles for swimming, legs for walking, 

 teeth for masticating food, just as they are now. In fact, 

 these primitive inhabitants of the antique world, however 

 diflerent in bodily shape from those we see around us now, 

 lived under the same universal laws of physiology as we 

 ourselves do."* To this it may be added, that these animals 

 of the past hved, too, under the same general inorganic 

 conditions as those in which we have our being. 



But this conclusion, most momentous and far-reaching 

 though it be, seems strangely overlooked by both text-book 

 and popular writers on geology. It may, therefore, be 

 well to briefly emphasize the undoubted teaching of the 

 facts presented by a study of the Cambrian rocks. 



These facts are some petrological and some palreonto- 

 logical. 



The Cambrian rocks are not only of vast thickness, but 

 they form extensive areas both numerous and widely 

 dispersed. In the British Islands they are conspicuous 

 in Wales, whence they take their name, in Shropshire, 

 Cumberland, Scotland, Ireland, and the Isle of Man ; and 

 on the Continent of Europe we find them in France, 

 Belgium, Germany, Bohemia, and Spain, and far north in 

 Sweden and Norway. In the western continent they form 

 large areas in Canada, Nova Scotia, and the United States ; 

 and when we turn to the east we see these ancient rocks in 



* KeT. H. N. Hutchinson, " Creatures of Other Days," p. 2. 



far Cathay, for the Sinisian formation of China was shown 

 by Richthofen to be of Cambrian age. 



These enormous accumulations of marine sediment are 

 of very diverse character, presenting different lithological 

 aspects in different areas, and consisting, even in the same 

 area, of beds of greatly differing rocks. There are great 

 masses of sandstones, compacted and cemented aggregations 

 of grains of quartz derived from the destruction of still 

 older quartzose rocks, and there are also thick beds of 

 conglomerates made up of pebbles, every one of which has 

 been a water-rolled angular hard-rock fragment. There 

 are, too, immense accumulations of argillaceous rocks, 

 consisting altogether of materials derived ft-om the decom- 

 position of the felspar of granites or other felspathic 

 rocks, and there are, moreover, in America, calcareous 

 rocks, the material of which is the same as that forming 

 those newer limestones which have been the result of 

 organic action. Volcanic rocks, in addition, are not 

 wanting to furnish further evidence of what were the 

 cosmic conditions of the globe in the Cambrian period. 



But over and above all this, there are markings on 

 Cambrian sandstones identical with those now produced 

 by waves and ripples on sheltered shores and shallow- 

 water bottoms, as well as — and these are very significant 

 — cracks and pittings, only ascribable to the action of the 

 sun and rain. 



Such are, briefly stated, the main petrological facts of 

 the Cambrian rocks, and from these facts the followng 

 conclusions may be drawn : — 



Since the whole of the material of which these rocks of 

 enormous thickness and of diverse mineral character has 

 been accumulated by the deposition of derived matter on 

 sea-bottoms exactly as marine sediments are now being 

 accumulated, it follows that those agencies of Natm-e, 

 which are the controlling forces of the physical cosmos, 

 were acting in the same way as at present. 



Not only do we see that the matter of the globe was the 

 same in its chemical combinations and states of aggregation 

 as now, but that the bulk of the water of the globe was in 

 a liquid state, and that therefore the temperature over the 

 greater part of the earth was, as at present, between 82^^ 

 and 212- Fahr. 



The derivation of the material of the sediments required 

 the erosion of land smrfaces by water agency, requiring rain, 

 which again required the atmosphere to be charged with 

 varying amounts of water-vapour, increased at one time by 

 evaporation and at anothertime diminished by condensation. 

 Thus there was rain that formed streams and rivers on 

 the land, that wore down and destroyed rocks, the detritus 

 of which was transported to the sea, in aU respects exactly 

 as at present. Thus, too, there were alternations of 

 temperature to produce alternate evaporation and conden- 

 sation, and those alternations were confined for the most 

 part within very moderate limits as now. 



Clouds, too, would form, wax and wane, and, with 

 varying densities of aggregation of the watery particles, 

 assume those beautiful forms we know so well, and float at 

 various elevations in the atmosphere ; and when these 

 clouds broke or dissolved, blue skies and bright sunshine 

 would alternate with shade even as now. 



Again, the air would be put in motion by the varying 

 temperatures, and consequently winds would sweep the land 

 and ripple the sea, waves would beat upon the shores and 

 roll rock-fragments into smooth rounded pebbles. These 

 winds with the rotation of the earth would take the courses 

 they now have, and so there would be then as now trade- 

 winds and anti-trades as well as cyclones and hurricanes, 

 and the monsoons and calms of the tropics. There would 

 also be ocean currents, that would mingle the waters of the 



