550 Notices of Memoirs — Limestone an Index of Time. 



The author goes on to show that the area of granitic and volcanic 

 rocks in Europe and the part of Asia between the Caspian and the 

 Black Sea, as shown in Murchison's Map of Europe, is two-twenty- 

 fifths (-2V) of the whole ; much of this is probably remelted sedi- 

 ments, and some of the granites the product of metamorphism. 



From considerations stated at length, it is estimated that the area 

 of exposures of igneous to sedimentary rocks would be for all geo- 

 logical time liberally averaged at one-tenth {-^q) of the whole. 



These igneous rocks are either the original materials of the globe 

 protruded upwards, or they are melted sediments or a mixture of the 

 two. 



The only igneous rocks we know of are of the nature of granites 

 and traps. If these rocks do not constitute the substratum of the 

 earth, and all known rocks, igneous as well as sedimentary, are 

 derivative, either geological time is infinite, or the rock from which 

 they are derived is, so far as we know, annihilated geologically 

 speaking, and we have no records of it left. 



If we assume the latter as true, the past is immeasurable, but in 

 order to arrive at a minimum age of the earth, the author starts from 

 the hypothesis that the fundamental rocks were granitic and 

 trappean. 



From eighteen analyses by Dr. Frankland, it is shown that the 

 water flowing from granitic and igneous rock districts in Great 

 Britain contains on an average 3-73 parts per 100,000 of sulphates 

 and carbonates of lime. 



The amount of water that runs off the ground is given for several 

 of the great continental river basins in Europe, Asia, Africa, and 

 America. The annual depth of rain running off the granitic and 

 igneous rock areas, taking into consideration the greater height at 

 which they usually lie and the possibility of greater rainfall in 

 earlier ages, is averaged at 28 inches, and the annual contribution of 

 lime in solution in the forms of carbonates and sulphates at 70 tons 

 per square mile. 



With these elements, and giving due weight to certain physical 

 considerations that have been urged in limitation of the earth's age, 

 the author proceeds to his calculations, arriving at this result, that 

 the elimination of the calcareous matter contained in the sedimentary 

 crust of the earth must have occupied at least 600 millions of years. 

 The actual time occupied in the formation of the groups of strata as 

 divided into relative ages by Prof. Kamsay, is inferred as follows : — 



Millions of Years. 



Laurentian, Cambrian, and Silurian 200 



Old Red, Carboniferous, Permian, and New Red 200 



Jurassic, Wealden, Cretaceous, Eocene, Miocene, Pliocene, 



and Post-Pliocene 200 



600 



The concluding part of the paper consists of answers to objections. 

 The author contends that the facts adduced prove geological time to 

 be enormously in excess of the limits urged by some physicists, and 

 ample to allow on the hypothesis of evolution for all the changes 

 which have taken place in the organic world. 



