681 



considered, both from its structure and its fossils, as near the doubt- 

 ful limit between the Upper Cambrian and Lower Silurian Systems. 



II. Culm measures. — This series is described (as in a former paper) 

 to occupy a great trough, which ranges across the country in a di- 

 rection bearing nearly east and west ; on its north side overlying 

 the preceding group (No. 6. of the North Devon section), and 

 on its south side rising up to the granite of Dartmoor, or overlying 

 the older slate system of Devonshire and Cornwall*. Its subdivi- 

 sions are enumerated as in the former paper ; and the author adds, 

 that during the summer of 1837 he ascertained that the lower beds 

 of the culm measures rest unconformably on a portion of the slate 

 rocks in the north of Cornwall, near Launceston. On the contrary, 

 in the cliffs near Barnstaple, the lower culm measures seem to gra- 

 duate almost insensibly into the formation on which it rests. Hence 

 (independently of all other evidence) it is clear that slate rocks in 

 the north of Cornwall are of an older epoch than the upper group 

 of thg North Devon section. 



The author then considers the classification of the culm series, and 

 states his opinion that the base of it is lower than the base of the 

 ordinary English carboniferous series. The base line (in the former 

 paper) was, intentionally left in an ambiguous position ; and the dif- 

 ficulty of the subject has been subsequently increased by the supposed 

 discovery of some true carboniferous plants in the highest group 

 (No. 6.) of the North Devon section. In the upper part of the culm 

 measures all the fossil plants have been described as identical in spe- 

 cies with plants of the carboniferous series ; and hence (unless some 

 conflicting evidence be discovered) the culm measures and common 

 coal measures must continue to be placed on the same parallel. 



Lastly, he states that, independently of any question of classifica- 

 tion, the former paper by Mr. Murchison and himself first pointed 

 out the following facts in the general structure of the county : — 



(1.) That the WaveUite rock and culm limestone (of Barnstaple, 

 &c.) w^ere ia position, structure, and fossils distinct from all the other 

 calcareous groups of Devon. 



(2.) That the same group was repeated over again w^ith a reversed 

 dip on the north side of Dartmoor, and entirely distinct from the calca- 

 reous slates of Cornwall, with which it had no analogy in structure 

 or fossils. 



(3.) That the Holcombe Rogus limestone was a part of the culm 

 series. 



(4.) That the culmiferous system was superior to all the slate rocks 

 of Devonshire and Cornwall, and was overlaid by no older rock than 

 the new red sandstone. Whereas before, the portion of the culm 

 series near the granite had, from its metamorphic structure, been 

 confounded with the oldest rocks of Devonshire and Cornwall ; and 

 the position of whole series among the Devonian groups had been 

 misapprehended. 



See Proceedings, p. 561. 



