§11. THE TERTIARY FORMATIONS. 213 



In some of the examples quoted, the surface of the 

 country is not unfavourable to the passage of such materials 

 as compose the drift, if urged on by floods or sudden rushes 

 of water ; and if it be assumed that the Cumberland moun- 

 tains were of sufficient altitude, during the boulder period, 

 to accumulate glaciers, the torrents produced by the melting 

 of the ice in the summer seasons, would account for some of 

 these beds of transport. But in many instances the physical 

 configuration of the surface forbids this interpretation ; and 

 the subaqueous condition of the country, and the action of 

 currents, waves of translation, and ice-floes, offer the most 

 satisfactory explanation of the phenomena.* 



11. The Tertiary Formations. — We now enter upon 

 the consideration of the Tertiary Formations, — those 

 ancient deposits of seas, rivers, and lakes, which belong 

 to the period immediately antecedent to that which is 

 marked by the prevalence of existing species of quadru- 

 peds, and of extinct elephantine forms, as the Mammoth, 

 Mastodon, &c. and subsequent to the deposition of the 

 uppermost secondary formation, the Chalk. 



The discoveries of MM. Cuvier and Brongniart, about 

 thirty years since, in the immediate vicinity of Paris, first 



review of some of the principal examples of drift in that part of 

 England. The young geologist in perusing this memoir must, how- 

 ever, bear in mind, that the facts so graphically described, do not afford 

 any evidence of a recent universal deluge ; a hypothesis maintained 

 by the most eminent geologists of that period (1821). 



* Our limits will not admit of any further notice of the erratic blocks 

 of England ; but it may interest the reader to know that there is a 

 very instructive example of a ridge of drift, probably deposited by an 

 ics-floe, in the immediate vicinity of Loudon, namely, Muswell Hill, 

 beyond Highgate ; which is capped with an alluvial bed of pebbles, 

 boulders, and fossils of rocks of all ages, from the chalk to below the 

 carboniferous limestone inclusive. The collections of Mr. Wetherell 

 and Mr. Toulmin Smith, of Highgate, contain characteristic fossils of 

 the oolite, lias, mountain limestone, &c, with blocks and pebbles of 

 granite, gneiss, and other primary rocks, all obtained from Muswell Hill. 



