14 MR. E. A. NEWELL ARBER ON" THE UPPER [Feb. I907, 



probably identical with the concretionary structures described here 

 as calcareous nodules, which, both in their composition and in their 

 included fossils, differ entirely from true clay-ironstone nodules, and 

 agree remarkably with the nodular concretions of marine origin 

 found in North Staffordshire, Yorkshire, and Lancashire. 



The calcareous nodules found in Devon and Cornwall nearly 

 always occur in thin beds of shale, which are 2 to 3 feet thick, or more 

 rarely of greater extent. The nodules vary much in shape and size. 

 The smaller tend to be somewhat globular, the larger are more 

 oval or biconvex in shape. A small nodule may be only 2 inches 

 along its greatest diameter, while a larger one may exceed a foot 

 in length : a length of about 6 inches being an average size. The 

 weathered surface is often somewhat iron-stained, and tends to 

 flake off. They are of a compact texture, hard to the hammer, and 

 break irregularly. They usually effervesce freely on the application 

 of dilute acid. Other nodules, however, also occur which are 

 apparently not calcareous, although closely similar to those under 

 •discussion. 



The calcareous nodules commonly contain a marine fauna. Casts 

 of goniatites are common, the cast being often filled with calcite. 

 Impressions of lamellibranchs are not infrequent, and, like the 

 goniatites, are irregularly distributed in the nodule. An account 

 of this fauna will be given at a later stage in this paper (p. 23). 

 Obscure plant-fragments are occasionally associated. 



Mr. Howe has kindly examined one or two typical nodules for 

 me. An example from the north side of Lower Sharpnose Point 

 in Cornwall, is a fine-grained, muddy sandstone, with a little mica : 

 there being enough calcareous cement to cause mild effervescence. 

 Another, also obtained in situ on the west side of Clovelly Harbour, 

 is a siiicified mudstone : it might be called an impure chert. There 

 is a certain amount of calcareous cement, but not much, and the 

 rock scratches glass. A third nodule, containing indications of 

 goniatites, found under Gallantry Bower, north-west of Clovelly, 

 proves to be scarcely calcareous at all, but is probably a decomposed 

 example of a rock like that from Clovelly Harbour. 



It would appear that most of the Upper Carboniferous rocks in 

 Devon and Cornwall contain a little calcite. McMahon 1 found 

 evidence of this mineral in the beds near Bude, and states that 

 veins occur in these rocks stopped with calcite. Probably the 

 amount varies locally, and, where more abundant, the mineral 

 appears to be aggregated into nodular forms or into lenticular bands. 

 The impression left by a detailed examination of the Devon and 

 Cornish coast-line, without however any special petrological study 

 of the beds, is that transitions may probably be found from beds 

 containing little or no calcite to concretionary beds of calcareous 

 nodules, and even to thin, inconstant, and impure limestone- 

 bands. 2 



1 McMahon (90) p. 109. 



2 Compare the characters of the Pendleside Limestones, Hind & Howe (01) 

 p. 395, &c. 



