346 STKATIGRAPHICAL GEOLOGY 



covered by snow in the winter, and that fragments falling on this 

 snow-slope slide down to its outer edge. This process is repeated 

 year by year, so that the talus fringe is continually being extended, 

 and blocks of large size are conveyed to a much greater distance 

 from their sources than would be possible without the snow-slope. 



Another accompaniment of this Permian upheaval was the 

 outbreak of volcanic action and . the establishment of numerous 

 volcanoes, from which frequent eruptions of lavas and ashes took 

 place. Nor are there wanting evidences of earthquakes, especially 

 in Devonshire, where round Brixham and Torbay the Devonian 

 limestones are riven by fissures from a few inches to 3 feet in width, 

 and these are filled with red sandstone similar to the Permian 

 sandstones, of which patches still remain on the surface of the 

 limestone plateau. 



This epoch of high elevation may have lasted for a long time, 

 but at length another change took place ; volcanic activity ceased, 

 and as so often happens in such cases a general sinking in and 

 subsidence ensued. Some of the great plains on which the red 

 sandstones and breccias had been accumulated sank below sea-level, 

 and were invaded by the Eastern Sea, becoming a large gulf or land- 

 locked " Mediterranean " sea in which deposits of dolomitic lime- 

 stone, shale, and marl were formed. 



Toward the close of the period, however, this inland sea became 

 isolated, probably by local warping and other irregular crust-move- 

 ments, so that it was cut off from the outer sea and converted into 

 a great salt lake like the Caspian Sea of the present time. From 

 time to time during dry seasons portions of this sea were dried up, 

 and the salts in solution were precipitated to form the thick masses 

 of gypsum and rock-salt which are such conspicuous members of the 

 highest Permian deposits. 



EEFERENCES 



1 Cantrill, Quart. Journ. Geol. Soc. vol. li. p. 528. 



2 King, Quart. Journ. Geol. Soc. vol. Iv. p. 97. 



3 H. T. Brown, Quart. Journ. Geol. Soc. vol. xlv. p. 22. 



4 Bonney, Midland Nat. vol. xv. p. 25 (1892) ; and Quart. Journ. Geol. 

 Soc. vol. Iviii. p. 18S. 



5 Reinach in Ussher, Geol. Mag. vol. xviii. 



6 Ussher, Quart. Journ. Geol. Soc. vol. xxxiv. p. 459. 



7 Woolacott, Quart. Journ. Geol. Soc. vol. Ixvii. p. 312. 



8 Hickling, Mem. Manch. Lit. and Phil. Soc., 1909. 



9 Watson, Geol. Mag., 1909, p. 102. 



10 Nikitin, Gongris geol. internal. (1897), Guides Nos. 1 and 2. 



11 Sibertzew, Mem. Com. Geol. Russe, xv. (1899). 



12 Amalitsky in Geol. Mag., 1901, p. 231. 



13 Bonney, Quart. Journ. Geol. Soc. vol. Iviii. p. 185. 



