SIR RODERICK J. MURCHISON. U)9 



departments. The work was appropriately dedicated to 

 his friend and fellow-traveller Sedgwick. Before the 

 publication of this truly great work, these Gray \va eke 

 rocks had generally been looked upon as a geological 

 chaos, but Murchison had now succeeded in mapping 

 off the order of their upper divisions, and in revealing 

 to his readers a series of changes in the fossil groups 

 of life, analogous to those which William Smith had 

 proved to exist in the secondary rocks. He had. 

 moreover, traced the flows of lava and basalt, and the 

 sheet of volcanic ash to the sites from which they were 

 poured forth ; and he had proved to what a thickness 

 the volcanic detritus had spread over the ancient 

 Silurian Sea. 



Before the " Silurian System " was well out of his 

 hands, Murchison, in conjunction with Sedgwick, deter- 

 mined to make out the history of the rocks of Devon- 

 shire and Cornwall. Their labours resulted in the 

 proof that the massive slate rocks of the south-west of 

 England, and the irregular fossil coral reefs at Torquay, 

 Plymouth, and elsewhere, formed part of a group of 

 strata below the coal measures and later than the 

 Silurians. 



After a hasty, but most successful tour in France, 

 Murchison determined to employ himself in an under- 

 taking more serious than anything he had previously 

 done. This was to strike across the Russian empire to 

 the Urals, and his plan was welcomed by the Russian 

 Government with promises of support. In the spring 

 of 1841, accompanied by M. de Verneuil, he bent his 

 steps towards the Neva. The Emperor himself took 



