GEOLOGICAL TIME.

Globe, Volume XXI, Issue 1801, 28 November 1879, Page 3

GEOLOGICAL TIME.

Geologists, astronomers, and physicists alike have hitherto been baffled in their attempts to set up any satisfactory kind of chronometer which will approximately meaanre geological time, and thus give us some clue to the antiquity of our globe. It is therefore worth noting that Mr Mellard Beade, of Liverpool, has lately contributed to the Royal Society a very suggestive paper, in which he endeavors to grapple with the question by employing the limestone rocks of flie earth's crust as an index to geological time. Limestones have been in course of formation from the earliest known geological periods, but it would appear that the later found strata are m"re calcareous than the earlier, and that there has been a gradually progressive increase of calcareous matter. The very extensive deposition of carbonate of lime over wide areas of the ocean bottom at the present day is sufficiently attested by the recent soundings of the Challenger, According to the author's estimate, the sedimentary crust of the earth is at least one mile in average actual thickness, of which probably one-tenth consists of_ cal- • careous matter. In seeking the origin of this calcareous matter, it is assumed that the primitive rocks of the original crust were of the nature of granite or basaltic rocks. By the disintegration of such rocks, calcareous and other sedimentary deposits have been formed. Trie amount of lime salts in water which drains districts made up of granites and basalts is found, by a comparison of analyses, to be on an average about 3 73 parts in 100,000 parts of water. It is further assumed that the excessed areas of igneous rocks, taking an average throughout all geological time, will bear to the exposures of sedimentary rocks a ratio of about one to nine. From these and other data, Mr Beade concludes that the elimination of the calcareous matter now found in all the sedimentary strata must have occupied at least 600,000,000 of years. This, therefore, represents the minimum age of the world. The author infers that the formation of the Lautentian, Cambrian, and Silurian strata must have occupied about 200,000,000 of years; the Old Bed Sandstone, the Carboniferous, and the Poikilitio systems, another 200,000,000; and all the other strata, the remaining 200,000,000. Mr Beade is, therefore, led to believe that geological time has been enormously iu excess of the limits urged by certain physicists ; that it has been ample to allow for all the changes which, on the hypothesis of evolution, have occurred in the organic world.