230 



ICE-ACTION IN THE DEVONIAN PERIOD. 



[Ck. XL 



or six feet, and are therefore most comparable, in size at 

 least, to crustaceans now living in Japan, and in regions still 

 nearer the equator. The mollusca and corals resemble gene- 

 rically those of the Carboniferous period. The Devonian 

 flora is chiefly known to us through the labours of American 

 geologists in the State of New York, and in Canada as far 



north as lat. 49°. More than sixty American species are 

 enumerated b} r Dr. Dawson from that continent, and they com- 

 prise, as we have seen (p. 149), so large a portion of the car- 

 boniferous genera, as to point to a similarity of climate. 

 The same may be said of the European plants of corre- 

 sponding age, so far as they are known. 



Supposed signs of ice-action in the Old Bed Sandstone, or 

 Devonian Period. — The Rev. J. C. Cumming, in 1848, in his 

 History of the Isle of Man, compared the conglomerate of the 

 Old Red Sandstone to 'a consolidated ancient boulder clay; 5 

 and more recently (1866), Professor Ramsay has pointed out 

 that the conglomerate of the same age seen at Kirkby-Lons- 

 dale, and Sedbergli, in Westmoreland and Yorkshire, contains 

 stones and blocks distinctly scratched, and with longitudinal 



and cross striations, like the markings produced by glacial ac- 



tion. I have myself examined this rock, and have seen blocks 

 taken from it which exhibit such markings, some of them 

 undistinguishable from those which I have observed on blocks 

 taken from beneath a glacier. But Professor Ramsay has 

 himself adverted to the fact, that the conglomerate above 

 alluded to has been subjected to violent movements hi dif- 

 ferent directions, and to great pressure after it was buried 

 under thousands of feet of carboniferous strata. In con- 

 sequence of these movements, some markings have been pro- 

 duced within the body of the rock itself, one pebble having 

 occasionally been squeezed and forced against another, so as 

 to indent it. Many of the pebbles also, and stones two feet 

 and more in diameter, have acquired that polish which is 

 called slickenside ; and the same may be seen in various parts 

 of the marly matrix, and even in the layers of carbonate of 

 lime which have here and there been deposited in the inter- 

 stices between separate stones. Scarcely in any district of 

 England has there been a greater succession of rents and 





• 







r- 





I 



::, 





- 





ri 







* 



an i 



tyl 





I 



- 



mak 

 im 



7 • 









fga 



ul 



tin 









%V 



% 





■ 





I" 







* 





