Vol. 63.] CARBOXIFEKOUS ROCKS OF DEVON AND CORNWALL. 13 



impure limestones, were probably deposited in shallow water, and 

 thus differ, as to the conditions of deposition, from the more marine 

 type of goniatite-bearing limestone at Mouthmill, described above. 



(b) The Calcareous Nodules and their Fauna. 



In a previous note, Mr. Rogers and I 1 called attention to the 

 occurrence of calcareous nodules in the Upper Carboniferous beds of 

 Devon, containing a marine fauna similar to that which has been 

 found to occur elsewhere in the Coal Measures of Britain. 2 Since 

 the appearance of that paper, the distribution of these nodule-beds 

 has proved to be even more extensive than we were aware of at 

 that time. 



Nodular beds in the Upper Carboniferous rocks of Devon have 

 been briefly noticed by Sedgwick & Murchison, De la Beche, 

 Townshend Hall, and Ussher, but none of these observers were 

 apparently aware of their calcareous nature. De la Beche, 5 

 speaking of the Culm-beds of the Bideford district, states that 



' nodules of argillaceous ironstone are often found in the same localities with 

 the shale and anthracite, reminding us of the intermixture of iron-ores and 

 vegetable matter in the bogs and morasses of the present day.' [Further, he 

 speaks of] ' the shale with vegetable compressions and ironstone-nodules on the 

 north side of Cockington Head.' 



Sedgwick & Murchison 4 also noticed that 



' nodules of clay-ironstone are occasionally associated with the hard beds of 

 sandstone ; and sometimes they occur in beds, or rows, subordinate to the 

 shaky bands.' 



Townshend Hall,' 5 in 1876, described nodules from Instow in 

 North Devon, containing fish-remains and goniatites. In 1892 

 Mr. Ussher mentioned the occurrence of conglomeratic and con- 

 cretionary beds 6 in his detailed description of the coast-section of 

 the Bideford district. 



The nodular beds occurring in Devon, as in other Carboniferous 

 tracts, are greatly varied. Some nodules are soft, pure sandstone- 

 nodules, with a fair amount of iron, sometimes of a rusty-brown 

 colour when weathered. Others are hard shale-nodules, sometimes 

 also apparently containing a certain percentage of iron. But I 

 have never seen any specimen from Devon or Cornwall that at all 

 resembles the true clay-ironstone nodules, so common in the 

 Midland and Northern coalfields of England, in which well- 

 preserved plant-remains frequently occur. I am inclined to think 

 that the ' argillaceous ironstone ' of De la Beche and the ' clay- 

 ironstones ' of Sedgwick & Murchison mentioned above 7 are 



1 Eogers & Arber (04). 



2 Stobbs & Hind (05) ; also Stobbs (06). 



3 De la Beche (39) p. 125. 



4 Sedgwick & Murchison (40) p. 678. 



5 Hall (76). 



B Ussher (92) pp. 148, 149, & 153. 



7 Greenough, on his Geological Map of England, published in 1819, notices. 

 ' elay-ironstone ' near Clovelly. Probably these nodules were really calcareous, 

 like those which I have obtained at that locality. 



