10 ME. E. A. NEWELL AEBEE OX THE UPPER [Feb. I907, 



material of vegetable origin. On the contrary, plant-impressions 

 are abundant throughout, although extremely fragmentary, and 

 badly preserved. 1 There is little indication that their fragmentary 

 nature and decayed aspect are in any way due to the effects of the 

 folding and contortion which these rocks have undergone. The 

 most intelligible explanation appears to me to be that the material, 

 drifted from a neighbouring land-area, was deposited in a region sub- 

 ject to the action of strong currents. In the sandstones themselves, 

 current-markings are extremely frequent. The whole aspect of the 

 plant-remains is explained by the supposition that the vegetable 

 material was repeatedly tossed about and broken up by currents. 

 Such conditions also explain the decayed appearance of the fossils, 

 due to prolonged immersion before they became covered up in the 

 mud or sands of the estuary. The same currents would also tend 

 to sweep away and scatter far and wide any accumulation of 

 material, which if deposited in quieter waters might ultimately 

 have formed coal-seams. In the Bideford district only, the con- 

 ditions of deposition, for some reason or other, appear to have 

 been comparatively free from the disquieting influences of such 

 currents, and thus favourable for a sufficient accumulation of 

 material to form a coal-seam. The better preservation, and more 

 complete nature of the plant-remains in this district, supports 

 this conclusion, which, however, is opposed to that arrived at by 

 McMahon 3 | see p. 7 | from a study of the petrology of the Cornish 

 rocks. 



IV. The Calcareous Rocks. 



As the result of a close examination of the Upper Carboniferous 

 rocks of Devon and Cornwall, it has been found that calcareous 

 deposits, partly of marine and partly of freshwater origin, are much 

 more abundant than had been previously supposed. It is true that 

 Vancouver in 1808, and Sedgwick & Murchison in 1840, men- 

 tioned the fact that such beds are here and there associated with 

 the sandstones and shales : but. at a later period, it appears to have 

 been imagined that they probably belonged to some portion of the 

 Lower Carboniferous Series, in which limestones have been long 

 known to occur. At least, in 1885, we find Pengelly, 3 one of the 

 foremost of Devon geologists, positively asserting that such rocks 

 are unknown in the higher Carboniferous sediments of the Hartland 

 and Clovelly district. Both in Devon and Cornwall, however, not 

 only are concretionary beds, composed of calcareous nodules em- 

 bedded in shales, far from rare; but well marked, if impersistent 

 and inconstant, bands of impure limestone are also present. 



1 Sedgwick &c Murchison (40) p. 678. 



2 McMahon (90; pp. 112. 113. 



3 Pengelly (85) pp. 425-26. 



