754 T HE WONDERS OF GEOLOGY. Lect. VIII. 



strata — the Transition rocks, as they were termed ; till the 

 researches of Professor Sedgwick and Sir R. Murchison 

 ascertained their true position and relations, and the unity 

 of type which prevails in the organic remains of the entire 

 system, in places very distant from each other, and under 

 very dissimilar conditions of mineral character. The beauti- 

 ful coralline marbles of Babbicombe, Torquay, &c. (ante, 

 p. 643) belong to this formation. 



In Cornwall, which principally consists of Devonian strata, 

 with slates, and intrusive igneous rocks, Silurian deposits 

 have lately been detected. The killas, or metamorphic schists, 

 of the southern headlands of the coast, contain many fossils 

 typical of the Lower Silurian ; and Sir R. Murchison states 

 that the geological structure of Cornwall may now be 

 regarded as presenting the following series : — 



1. The lowermost : a band of Silurian deposits. 



2. A zone of an intermediate character, forming a transition between 



the Silurian and Devonian. 



3. A Devonian system characterized by lower and upper limestones. 



4. An extension of the culmiferous (carboniferous) strata of Devon- 



shire.* 



The killas are argillaceous strata that have been indu- 

 rated by metamorphic action, like those of Scandinavia and 

 the Ural mountains ; and as in those countries the granites 

 and porphyries of Cornwall, traverse the palaeozoic de- 

 posits. 



Sir R. Murchison further remarks, that the stanniferous 

 {tin) gravels of Cornwall bear the same relation to the 

 granite and killas, as the auriferous deposits of the Urals 

 to the erupted and schistose rocks of that chain. 



On the opposite side of the Channel, in Brittany and 

 Normandy, the same mineral type prevails ; namely, Cara- 

 doc sandstone and other Silurian, with Devonian and Carbo- 

 niferous strata. 



* Jameson's Edinburgh Journal for July, 1847. 



