RECENT WORK ON VOLCANOES 95 



must have had a far-reaching influence on the climate of the 

 world ; one can almost assert that it was this which was the 

 cause that enabled a tropical flora to flourish in the Eocene 

 period close to the North Pole, and that the epidemics con- 

 sequent on the pollution of the air were a factor at any rate in 

 the extermination of the Mesozoic types of animals. Not only 

 in North Europe and America were these volcanic outbursts 

 active, but in India the Deccan traps were extruded at about 

 the same time, and also probably the lavas of the Mawi 

 plateau in Central Africa. Contemporaneously with these 

 eruptions the crumpling of the earth's crust, which gave rise 

 to the Alps-Himalayan chains and the folds of the east of the 

 Pacific, was also started ; the vast dislocations of the earth's 

 crust and the floods of lava which issued from it in certain 

 parts, bring up the question whether this solid earth can con- 

 tain within itself such terrific forces of disruption ; or whether 

 it is not more reasonable, seeing that we have recently had 

 visitors from celestial space such as the planetoids Eros and 

 M.T., which, had they fallen upon the earth, would have caused 

 just such disturbances, to ascribe the early Cainozoic eruptions 

 and crumplings to causes operating from without. 



Volcanoes of Block-Uplift. — Reck (13) calls these Tafelberg- 

 horste, but in Iceland they always have a volcano on top. The 

 question whether they are horsts, that is, blocks from which 

 the neighbouring country has been faulted away, or whether 

 they owe their origin to vertical uplift, is a matter very difficult 

 to decide. In the Utah and Colorado plateaux, the whole 

 country is parcelled out in long strips and the difficulty of 

 explaining the occurrence here is as great one way as the 

 other. If the valleys between the long plateaux had been 

 faulted down, how could the strips between have been sus- 

 tained, with the earth's crust all shattered around them? It is 

 like the case of a pancake laid on a gridiron, but then the rods 

 of the gridiron are here represented by narrow slips of rock 

 fifty or more miles long, and these are not strong enough to 

 allow of suspension from the ends. Masses of igneous rock 

 pumped up by hydraulic pressure would supply an elevatory 

 force for the plateaux, and this seems a more reasonable 

 explanation ; hence these Colorado and Utah plateaux are still 

 called mountains of block-uplift. In the Ries (14) in Germany, 

 again, there is a circular depression some fifteen miles in 



