SCIENCE-GOSSIP. 



2/3- 



GEOLOGY 1% 



CONDUCTED BY EDWARD A. MARTIN, F.G.S. 



To whom all Sotts. Articles and material relating to Geology, 

 and intended for Science-Gossip, are, in the first instance, to 

 at 69, Bcnsham Manor Road. Thornton Heath. 



Foreign Stones in Chalk.— With reference to 

 the question of pebbles and boulders in the chalk, 

 Mr. A E. Salter. F.G.S., pointed out before the 

 Geological Society that smaller pebbles are fairly 

 numerous. The same pit from whence came the 

 Purley Boulder has yielded recently at least a 

 lozen specimens of various rocks, whilst others 

 have been obtained from Burham and Northfleet. 

 Fossil collectors might do well to search for 

 similar specimens. I shall be glad to hear from 

 any reader who has happened upon foreign stones 

 of any kind in the chalk. 



Age of the Earth. — Geologists are as inter- 

 ested as ever in the great question of the world's 

 age. Are we to accept, as did Prof. Huxley, the 

 dictum of the physicists, that we must include the 

 formation of all our stratified deposits without the 

 last 100,000,000 years ? There is apparently no 

 help but to do so. If so, it is interesting to bear 

 in mind the dates that have been assigned to 

 various formations by Dr. Croll in his "Climate 

 and Time." It is a quarter of a century since that 

 epoch-making book was published. Perhaps some 

 notes showing the conclusions to which he came, 

 may be useful to the younger geologists. 



Rate of Denudation.— Dr. Croll, after careful 

 consideration, estimated that the rate at which the 

 general surface of the globe is being lowered by 

 sub-aerial denudation could not be much less than 

 one foot in 0,000 years. He considered that what 

 is known as the Glacial Period coincided with a 

 period of great eccentricity of the earth's orbit, 

 which came to a close about 80,000 years ago. 

 Since that date, the surface of the earth at the 

 above rate of denudation would have been lowered 

 on the average by 13 feet. This total is, however, 

 not sufficient to remove the superficial glacial 

 accumulations, such as Karnes and Eskers, gravel 

 mounds, knolls of boulder clay, etc. 



Axe: CIATION. — Two other periods of 



great eccentricity terminated about 720,000 and 



■ars ago respectively ; but traces of 



ithout doubt, according 



II, at thoie times, would have been 



mpletely removed in the meantime. 



ue produced glacial | 



in Miocene and Eocene times respectively. 



The greatest 

 inion are held M to 



what consti- the gla< la 



I a country net ''f 



forma 4 ; lay in not thoroughly under. 



If r.auv 

 •hat if the:' 



v all, -m'.' 

 for I 

 In tocbacase. the boul-lcrn to which wcp 



last month as having been found in the chalk, may 

 be sufficient evidence of a veritable glacial epoch 

 occurring even in Cretaceous times. They may 

 show its principal effects on lands which have 

 since suffered extreme denudation, or which are 

 now still beneath the sea. Here, too, would be a 

 satisfactory explanation of those puzzling bands of 

 clayey-chalk which occur at all levels in the true 

 chalk, and to explain which it is impossible to 

 believe in repeated temporary shallowing of the 

 sea-bottom. Icebergs from the nearest coast might 

 well be the bearers of fine clay frozen in its mass. 



Geological Dates. — Our leading geologists are 

 seldom disposed nowadays to hazard certain dates 

 as those in which our principal formations were 

 laid down. Geologists of a past generation were 

 perhaps more speculative than we are. Sir Chas. 

 Lyell suggested dates in the world's history which 

 placed the earliest sedimentary formations far 

 beyond the limit allowed by our present physical 

 authority, Lord Kelvin. 



Age of Pre-Cambrian Series. — Dr. Croll 

 suggested that the Cambrian rocks may be but sixty 

 millions of years old. This estimate thus leaves 

 a great length of pre-Cambrian time in which to 

 allow of the evolution of life from probable lowly- 

 organized primitive forms to the varied fauna of 

 Cambrian age. Professor Ramsay has said that 

 in the life of the Cambrian age " we find no evi- 

 dence of its having lived near the beginning of the 

 zoological series. In a broad sense, all the phe- 

 nomena connected with this old period seem to my 

 mind to be of a quite recent description, and the 

 climates of seas and lands were of the very same 

 kind as those that the world enjoys at the present 

 day." 



Varying Distance of Sun. — The mean dis- 

 tance of the sun is now 91,400,000 miles. Its 

 present distance in mid-winter is Sq, 864,480 miles. 

 At Croll's suggested Miocene glacial epoch, 850,000 

 years ago, when the winter solstice was in peri- 

 helion, his distance in mid-winter would be no less 

 than 98,224,289 miles. " Our winters are now 

 shorter by 78 days than summers, but at that 

 period they would be longer than the summers. 

 by 347 days. ... At present the difference 

 between perihelion and aphelion distance of the 

 sun amounts to only 3,069,580 miles ; but at the 

 period under consideration it would amount to no 

 less than 13,648,579 miles." 



Intensity of Glacial Period. — Dr. Croll says : 

 " The more severe a glacial epoch is, the more 

 marked ought to be the character of its warm 

 inter-glacial periods. The greater the extension of 

 the ice during the cold periods of a glacial epoch 

 the further should that ice disappear in arctic 

 regions during the corresponding warm periods. 



... Judged by this test, we have every reason to 

 believe that the Miocene glacial epoch was one of 



extreme severity The Eocene period 



extends from about 2,620.000 to about 2,460,000 

 years ago ; and the Miocene period lasted from 

 about 980,000 to about 720,000 years ago." 



Ancient SUBMERGENCE. — Submer- 

 gence to as much as a thousand fwi during the 

 gUu lal epoch, explained by the transference of 



■ rap In. 111 '.Olltll to 1101 ill poll-, III.- 1 ' ill ' 



• , I', '.lull in." of earth 1 cut re ol gravity, 



and tli' ' ocean to adjust Itself as a 



sphere around that eentn ol gravity, On this 



Itlon submi end I the result, not "t 



.1 the land, bul ol a 1 tnenl ol 1 □< 



waters of the ocean t" r<l tin nortli 



