312 MAN AXD THE GLACIAL PERIOD. 



list of glacial observations in connection with rocks of a 

 remote age.* Beginning at the earliest date, he cites Pro- 

 fessor Archibald Geikie, one of the most competent judges, 

 as confident that the rounded knobs and knolls of Lauren- 

 tian rocks exposed over a large region in northwestern 

 Scotland, together with vast beds of coarse, angular, un- 

 stratified conglomerates, are unquestionable evidences of 

 glacial action at that early period. Masses of similar con- 

 glomerates, resembling consolidated glacial boulder-beds, 

 occur also in the Lower Silurian formation at Corswall, 

 England. In Dunbar, Scotland, Professor Forbes also 

 found, in formations of but little later age than the Coal 

 period, " brecciated conglomerates, consisting of pebbles 

 and large blocks of stone, generally angular, embedded in 

 a marly paste, in which some of the pebbles are as well 

 scratched as those found in medial moraines." In forma- 

 tions of corresponding antiquity the geologists of India 

 have found similar boulder-beds, in which some of the 

 blocks are polished and striated. 



Still, this evidence is less abundant than we should ex- 

 pect, if there had been the repeated Glacial epochs supposed 

 by Mr. Croll's astronomical theory ; and it is by no means 

 impossible that the conglomerates of scratched stones 

 described by Professor Ramsey in Great Britain, and by 

 Messrs. Blandford and Medlicott in India, may have re- 

 sulted from local glaciers coming down from mountain- 

 chains which have been since removed by erosion or subsi- 

 dence. We are not aware that any incontestable evidence 

 has been presented in America of any glaciation previous 

 to that of the Glacial period. 



Upon close consideration, also, it appears that Mr. 

 Croll's theory has not properly taken into account the 

 anomalous distribution of heat which we actually find to 

 take place on the surface of the earth. He has done good 



* Nature (August 26, 1880), vol. xsii, pp. 388, 389. 



