662 DE. G. J. HINDE AND ME. HOWAED FOX ON [Nov. 1895, 



term of Culm Measures, instead of being, as at present supposed, 

 an uniform series of shallow-water detrital deposits, really consist 

 of two groups of rocks, which in their nature and origin present 

 the widest possible differences. In the Lower Culm Measures, the 

 basal Posidonomya-be&s and the "Waddon Barton Beds with Goniatites 

 spiralis consist of fine shales and occasional thin limestones which 

 may have been formed in a moderately deep sea, but not beyond 

 the reach of the finer sediments brought from the land ; and over- 

 lying these are the Badiolarian Beds, mainly made up of these 

 organisms, and formed by the gradual accumulation of their remains 

 in a deeper sea too far removed from a land-surface for any but 

 the finest detrital particles to be carried out and mingled with 

 them. 



In the Upper Culm Measures, on the other hand, which are of 

 great thickness and extend over the greater part of the Culm area, 

 the beds consist of conglomerates, grits, sandstones, and shales, with 

 occasional thin bands of the Culm itself and plant-remains, which 

 show with sufficient clearness that this Upper Division has been 

 formed under shallow-water conditions. 



We are at present quite in the dark as to the nature of the 

 changes which set in after the deposition of the Badiolarian Beds ; 

 the conglomerates overlying these latter in certain areas give 

 evidence of an elevation and partial denudation of the Badiolarian 

 Beds at an early period in the history of the Upper Culm Measures. 



The additional fossils (excluding radiolaria) which we have 

 found in the Badiolarian Beds tend to confirm the view that these 

 and the Lower Posidonomya- and Waddon Barton Beds are the 

 representatives and equivalents of the Carboniferous Limestone in 

 other portions of the British Isles ; not, however, in the at present 

 generally understood sense that they are a shallow-water facies of 

 the presumed deeper-water Carboniferous Limestones, but altogether 

 the reverse, that they are the deep-water representatives of the 

 shallower-formed calcareous deposits to the north of them. Begarded 

 in this light, the occurrence of these Lower Culm Measures in Devon 

 and Cornwall, within about 30 miles of the great development of 

 Carboniferous Limestone in the Mendips to the north-west, no 

 longer presents such an anomaly as seemed to be the case when 

 they were believed to be of shallow-water formation. Under this 

 impression as to their character, Mr. A. J. Jukes-Browne * considers 

 that they indicate a muddy sea which received the sediments 

 brought down by large rivers draining continental land, which pro- 

 bably existed south-west of these areas, and the shore-line lay not 

 very far south of Devonshire. The picture, however, that we can 

 now draw of this period is that while the massive deposits of the 

 Carboniferous Limestone — formed of the skeletons of calcareous 

 organisms — were in process of growth in the seas to the north, 

 there existed to the south-west a deeper ocean in which siliceous 

 organisms predominated and formed these siliceous radiolarian 



1 ' Building of the British Isles,' 2nd ed. 1892, p. 139. 



