GEOLOGICAL TIME.

Globe, Volume XXI, Issue 1750, 29 September 1879, Page 3

GEOLOGICAL TIME.

Geologists, astronomers, and physicists alike have hitherto been baffled in their attempts to set up any satisfactory kind of chronometers which will approximately measure geological time, and thus afford us some clue to the antiquity of our globe. Mr Millard Beade, of Liverpool, has recently contributed to the Eoyal Society a very suggestive paper, in which ho endeavours to grapple with the question by employing tho limestone rocks of the earth’s crust as an index of geological time. Limestones have been in 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 faot, 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 Mr Beade’s estimate, the sedimentary crust of the earth is at least one mile in average actual thickness, of wkich probably one-tenth consists of calcareous matter. In seeking the origin of this calcareous matter, it is assumed that the primitive rooks of the original orust were of the 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 78 parts in 100,000 parts of water. It is further assumed that the exposed areas of igneous rocks, taking an average throughout all geological time, will bear to the exposures of sedimentary reeks 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 Lauretian, Cambrian, and Silurian strata, must have occupied about 200,000,000 years ; the old red sandstone, the carboniferous, and the poikilitio systems, another 200,000,00©; and all the other strata, the remaining 200,000,000. Mr Beade is, therefore, led to believe that geological time has been enormously in excess of the 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.