Vol. 6$.'] CARBONIFEROUS ROCKS OF DEVON AND CORNWALL. 25 



both freshwater and marine, the latter having a wide range 

 throughout the higher beds, is especially significant in this respect. 



Thus these Carboniferous rocks, described by Sedgwick & 

 Murchison as the Culm Measures, are not, for the most part, 

 of the same age as the Culm of the Continent. Only the lower 

 series, or Lower Culm Measures, is equivalent to the Culm of 

 Germany and Austria ; and this, in both Devon and Cornwall, is 

 of insignificant extent when compared with the upper division. 

 For this reason, it would seem advisable to avoid the use of the 

 term Culm Measures in the future when speaking of the British 

 rocks. 



It is also found that the differences in lithological and palseonto- 

 logical facies, which have been supposed to exist between the 

 Upper Carboniferous sequence in Devon and Cornwall and their 

 equivalents in other British coalfields, have been greatly ex- 

 aggerated in the past. The ordinary nomenclature is as applicable 

 to the Devon Basin as to any of our coalfields, and the Upper 

 Carboniferous sequence there is best described as barren Coal 

 Measures. Not only are the sandstones and shales of Devon 

 similar to those occurring in other basins, but calcareous rocks, 

 both of marine and of freshwater origin, are also associated. Two 

 faunas — the one marine, consisting of fish-remains, cephalopoda, and 

 lamellibranchs, and the other of freshwater lamellibranchs — have 

 been found at different horizons, and both these faunas are 

 common to other coalfields. Plant-remains are also distributed 

 abundantly throughout the series, although in Devon and Cornwall 

 they are nearly always fragmentary, and very badly preserved. 



In these respects, the Upper Carboniferous portion of the 

 succession in the South-West of England agrees with the Coal 

 Measures of the Midlands and the North. The chief differences 

 appear to be two in number. Except to a very limited extent in 

 North Devon, there is a remarkable absence of carbonaceous 

 deposits throughout the basin. This fact may probably be corre- 

 lated with the second point of contrast, namely, that the conditions 

 under which these sediments were accumulated was no doubt some- 

 what exceptional. So far as the state of the plant-remains will 

 permit us to arrive at any conclusion on this point, these rocks 

 appear to have been laid down in an area subject to the action of 

 strong currents, thus preventing a sufficient accumulation of 

 vegetable material in definite beds, which might eventually have 

 formed coal-seams. 



An examination of the coast-section of Devon and Cornwall has 

 led to the conclusion that the Upper Carboniferous sequence forms 

 one division lithologically, as it does palseontologically. Local 

 lithological types may be recognized here and there, but these are 

 not constant over any considerable area and tend to merge one 

 into the other. Thus the original twofold subdivision of the whole 

 Carboniferous Series, instituted by Sedgwick & Murchison, is main- 

 tained here, with the exception that the terms Upper Carboni- 

 ferous and Lower Carboniferous Series are substituted 



