THE AGE OF THE EARTH.

Globe, Volume XXI, Issue 1700, 1 August 1879, Page 2

THE AGE OF THE EARTH.

Geologists, astronomers, and physicists alike hare hitherto been baffled in their attempts to sot up any satisfactory kind of chronometers which will approximately measure geological time, and thus afford us some clew to the antiquity of our globe. Mr Millard Roado, ot Liverpool, has recently contributed to the Royal Society a very suggestive pap»r, in which he endeavours to grapple with the question by employing the limestone rocks of the earth's crust as an index of geological time. Limestones have been in the course of formation from the earliest known geological periods, but it would appear that the later formed strata are more calcareous than the earlier, and that there has, in fact, been a gradually progresssi ve 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 Mr Reade’s estimate, the sedimentary crust of the earth is at least one mile in average actual thickness, of which probably one tenth oonsisfs of calcareous matter. In seeking the origin of this calcareous matter, it is assumed that the primitive rocks of the original crust were of tho nature of granitic or basaltic rocks. By the disintegration of such rocks, calcareous and other sedimentary deposits have been formed. The amount of lime salts in water which drain districts made 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 exposed areas of igneous rocks, taking an average throughout all geological Lime, will bear to the exposures of sedimentary rocks a ratio of about one to nine. From these and other data Mr Reade ■ concludes that the elimination of the calcareous matter now found in all the sedimentary strata must have occupied at least 600 millions of years. This, therefore, represents the minimum aea of the world. The author infers that the formation of the Lauretian, Cambrian, and Silurian strata must have occupied about 200 millions of years ; the old red sandstone, the carboniferous, and the poikilitio systems, another 200 millions; and all the other strata, the remaining £OO millions. Mr Reade is, therefore, led to believe that geological time ha* been enormously in excess of tho limits urged by certain physicists ; and that it has been ample to allow for all the changes which, on the hypothesis of evolution, have occurred in the organic world.