ADDRESS. 17 



is 40 feet thick, and underneatli it there is a bed of clay, with rootlets, 

 quite comparable to the underclay which is found beneath almost every 

 bed of coal in the British and other coal-fields of the Carboniferous epoch. 

 The Miocene rocks of Switzerland are familiar to all geologists, who have 

 traversed the country between the Jura and the Alps. Sometimes they 

 are soft and incoherent, sometimes formed of sandstones, and some- 

 times of conglomerates, as on the Righi. They chiefly consist of fresh- 

 water lacustrine strata, with some minor marine interstratifications which 

 mark the influx of the sea during occasional partial submergences of 

 portions of the area. These fresh- water strata, of great extent and thick- 

 ness, contain beds of lignite, and are remarkable for the relics of numerous 

 trees and other plants which have been described by Prof. Heer of 

 Zui'ich, with his accustomed skill. The Miocene fresh-water strata, of the 

 Sewalik Hills in India are well known to most students of geology, and I 

 have already stated that they bear the same relation to the more ancient 

 Himalayan mountains that the Miocene strata of Switzerland and the 

 North of Italy do to the pre-existing range of the Alps. In fact, it may be 

 safely inferred that something far more than the rudiments of our present 

 continents existed long before Miocene times, and this accounts for the 

 large areas on those continents which are frequently occupied by Miocene 

 fresh-water strata. With the marine formations of Miocene age this 

 address is in no way concerned, nor is it essential to my argument to deal 

 with those later tertiary phenomena, which in their upper stages so 

 easily merge into the existing state of the world. 



Olacial Phenomena. 



I now come to the last special subject for discussion in this address, 

 viz., the Recurrence of Glacial Epochs, a subject still considered by some 

 to be heretical, and which was generally looked upon as an absurd crotchet 

 when, in 1855, I first described to the Geological Society, boulder-beds, 

 containing ice-scratched stones, and en-atic blocks in the Permian strata 

 of England. The same idea I afterwards applied to some of the Old 

 Red Sandstone conglomerates, and of late years it has become so familiar, 

 that the effects of glaciers have at length been noted by geologists from 

 older Palaezoic epochs down to the present day. 



In the middle of last July I received a letter from Prof. Geikie, in 

 which he informed me that he had discovered mammilated moutonnee 

 surfaces of Laurentian rocks, passing underneath the Cambrian sand- 

 stones of the north-west of Scotland at intervals, all the way from Cape 

 Wrath to Loch Torridon, for a distance of about 90 miles. The mammi- 

 lated rocks are, says Prof Geikie, ' as well rounded off as any recent roclie 

 moutonnee,' and, ' in one place these bosses are covered by'a huge angular 

 breccia of this old gneiss (Laurentian) with blocks sometimes five or six 

 feet long.' This breccia, where it occurs, forms the base of the Cambrian 

 strata of Sutherland, Ross, and Cromarty, and while the higher strata are 

 1880. c 



