Physical Structure and older stratified Deposits of Devonshire. 689 



same may^, we believe^, be said generally of the arrangement given by Mr. 

 Williams. We shall, therefore^ for the future, refer to the successive groups 

 in the North Devon section with entire confidence. The only questions 

 which can now arise, must refer to their age and classification, — not to their 

 relative position. 



To our four sections, illustrating the structure of South Devon, we make no 

 material change or addition ; with one exception, however, viz. the interpola- 

 tion of a small band of culm measures between the Ashburton limestone and 

 the granite — discovered by Mr. Austen since our visit in 1836, and repre- 

 sented (PI. LI., fig. 8.) on his authority, as has indeed been already stated 

 in a note to our former paper. Neither have we any material change to make 

 in our comparison of the deposits of North and South Devon. Considered 

 as a whole, we still think that they belong to one system of formation ; and 

 that the lowest group of South Devon is lower than the lowest group of North 

 Devon. But as for our comparison of the subordinate groups (though still 

 the best that we can offer), we only throw it out as provisional, being chiefly 

 founded on mineralogical characters, and those perhaps not of a very conclu- 

 sive kind. 



Lastly, we have no change to make in our description of the fossiliferous 

 groups of Cornwall. They are very nearly on a parallel with groups exhi- 

 bited in the sections of North and South Devon ; and the fossiliferous slates 

 of both counties belong to one system. We do not encumber ourselves with 

 any details respecting the more crystalline and (as we believe) altered slates ; 

 but we have, in our former paper, shown that they are not, merely on account 

 of their structure, to be regarded as older than the calcareous and arena- 

 ceous deposits. 



After these preliminary remarks we proceed (agreeably to a promise given 

 in our former paper) to re-examine the classification of the respective groups 

 inferior to the culm measures ; and we begin by expressing our entire con- 

 viction that the true equivalents in the several disjointed sections can only 

 be made out by zoological evidence. 



We were at first led to the opinion, that the series of deposits we are de- 

 scribing, were to be placed below the Silurian system, partly from the re- 

 semblance of the highest group (No. 3 of the North Devon section) to the 

 Caradoc sandstone; and perhaps still more from the mineral structure and 

 slaty cleavage of many parts of the lower groups. At that time we had not 

 sufficient boldness to adopt the only other alternative, and throw all the old 

 slates of Devon, and the (supposed) primary slates of Cornwall, into the epoch 



