Vol. 63.] CAEBONIFEROUS ROCKS OP DEVON ANJ) CORNWALL. 11 



(a) The Impure Limestone-Bands. 



Vancouver, 1 in his * Agriculture of the County of Devon,' pub- 

 lished in 1808, mentions the occurrence of these limestones in a 

 number of localities, some of which, such as Chittlehampton, 

 Bishop's Nympton, King's Nympton, and Eomansleigh, etc., are 

 situated on Upper Carboniferous rocks. He states that the lime- 

 stones have been worked in certain of these places. 



Sedgwick & Murchison 2 remark that 



' among the accidental beds we may also notice calcareous shale passing into 

 thin, impure bands of limestone, of which we saw an example near Hather- 

 leigh.' [Also that] ' similar thin impure beds of limestone are found in several 

 other places in the upper culm-measures.' 



These localities all lie considerably to the east of the district 

 described here, and I have not visited any of them. It seems, 

 however, clear that the occasional occurrence of thin limestone- 

 bands in the Upper Carboniferous rocks of North Devon was 

 known before 1808, although this fact appears to have been lost 

 sight of in more recent times. 



In a short note, published in 1904, 3 1 announced the discovery, 

 by Mr. Eogers, of a well-marked limestone-band, exposed in a 

 sharp anticlinal fold, to be seen in the coast-section a short distance 

 (about 300 yards) east of Mouthmill and Blackchurch Rock, and 

 between 1^ and 2 miles along the coast north-west of Clovelly. 

 This band may be spoken of as the Mouthmill Limestone. It 

 overlies a thick shale-bed containing a very large number of calcareous 

 nodules of all sizes, especially in the upper layers where it adjoins 

 the limestone. The limestone on the north side varies from 9 to 20 

 inches in thickness. On the south side of the anticline, it isimper- 

 sistent, and soon disappears altogether. Sections of the limestone 

 were kindly examined for me by Mr. J. A. Howe, F.Gr.S., who 

 pronounced the rock to be an impure limestone. The limestone, as 

 well as the nodules in the shale-bed below, contains numerous 

 goniatites, in the form of casts often filled with calcite, as well as 

 other fossils (p. 24). The origin of the limestone appears to be 

 similar to that of the calcareous nodules ; but, the lime being more 

 abundant in the first case, a definite band has been formed. 



Although the Mouthmill Limestone remains the best example of 

 a limestone that I have seen from the Upper Carboniferous sequence 

 of Devon, other but highly -impure bands have been subsequently 

 discovered, and probably such rocks are not infrequent throughout 

 the extent of these beds. In July 1904, Mr. Eogers, while re- 

 examining the coast-section of Cornborough Cliffs between West- 

 ward Ho ! and Greenacliff in North Devon, recognized a number of 

 lenticular bands of impure limestone. More than twenty have 

 since been identified. The lenticular form of these beds is very 



1 Vancouver (1808) pp. 57-63. 



3 Sedgwick & Murchison (40) p. 678 ; and footnote on pp. 678-79. 



s Rogers & Arber (04). 



