LAST ELEVATION POSTERIOR TO THE LIAS. 



299 



In the meantime, by completing the observations in one region, it has been proved, 

 that volcanic matter was emitted for a very long time during the formation of the 

 Silurian strata, and that afterwards other eruptions took place, throwing those ancient 

 strata into vertical, undulating, and broken masses, and probably giving rise to metal- 

 liferous veins ; that the coal measures were accumulated after the last-mentioned pe- 

 riod of disturbance, because they rest unconformably upon the inclined edges of the 

 Silurian rocks ; and lastly, that other volcanic forces, evolving products similar in 

 lithological structure to those previously erupted, renewed their activity on the same 

 lines of fissure after the accumulation of the New Red Sandstone and even of the Lias. 



