48 RAMBLES AND REVERIES. 



brachiopods and trilobites enable the age of the 

 beds to be discovered. 



DEVONIAN. The beds of this age consist of the 

 well-known Killas, and through them vast bosses 

 of granite have burst their way. On St. Michael's 

 Mount, the junction of the granite and the Killas 

 was distinctly traced out for us by Sir W. W. 

 Smyth, who, in this excursion, conducted our party, 

 and entertained us at his summer villa close by. 



CARBONIFEROUS. These are the Cornish "culm- 

 measures," and are situated on the north coast, too 

 far out of our line of march to be visited. 



Until recently, no formation has been known in 

 Cornwall newer than the Palaeozoic, unless some of 

 the " elvans " or dykes of quartz-porphyry running 

 out from the granite be newer, as they certainly 

 are more recent than the granite which has burst 

 through the Devonian Killas. But, within the last 

 few years, a most interesting bed has been dis- 

 covered near St. Erth. While digging for clay for 

 the Penzance dock, a number of marine shells were 

 met with. These turned out to be identical with 

 the fossils of the Pliocene or Red Crag, which 

 every visitor to Walton-on-the-Naze has seen. 

 Here a busy hour was spent by our company ; and 

 I was able to obtain a good supply of Nassa, 

 Turritella, and a few other things. Can it be that 

 this deposit means that the sea, so recently as the 

 Pliocene age, stretched from the Atlantic away to 

 the Mediterranean, where similar fossils are found, 

 and that the deposits of the crag period have since 

 been denuded from the entire tract of country 



