276 H. J. Lowe — Devonshire Geology. 



square miles of surface within the narrow limits of one unit of 

 geologic time. Does not the supposition provoke the question of 

 possibility in place of probability ? 



Another consideration suggested by the 'lagoon' hypothesis is 

 the remarkable thickness of the clay beds on the western side so 

 near the source of origin. The material of the clay derived from 

 the decomposition of the felspars of the granite is of extreme 

 fineness, probably the most impalpable material forming deposits, 

 so that it would be held in suspension longer than any other detrital 

 material, and would be precipitated only where the water was 

 almost, if not quite, motionless. 



Consequently it does not seem to be consistent with the nature of 

 the material in suspension that such an enormous deposit should 

 have been made close to the foot of the steep slopes of the granite, 

 where the rapid streams bearing the detritus would cause continual 

 commotion and currents that would make themselves felt for con- 

 siderable distances in a large tideless water area ; so that the 

 deposition of the finest material would hardly take place quite near 

 to the stream discharges without some check to the motion of the 

 water such as narrower land boundaries would give. One would 

 therefore expect to find the finest and purest clay in thickest beds 

 away from that part of the ' lagoon ' where the streams entered it, 

 while the coarser material would indicate that locality. The sands 

 could scarcely reach the farther part of the basin until the western 

 part was shallow enough to allow the streams to retain suificient 

 carrying power to convey them. But this arrangement is not found 

 in the fresh-water deposits of the Hampshire basin, and indeed 

 Mr. Gardner accounts for the way they occur rather by current action 

 in an estuary than by deposition in an entirely water-covered area. 

 The same line of thought occurs in connection with the 31 super- 

 imposed lignite beds found so near the discharging place of the 

 streams. If there had been a much larger sheet of water than the 

 Bovey area comprises, would it not be likely that the drift vegetation 

 forming the lignite beds would have floated farther away before 

 becoming waterlogged and settling down with the fine clay material ? 

 In respect to the point whether the waters of Dartmoor did 

 convej' the Eocene deposits to the Hampshire basin there seems 

 to be an almost absolute criterion, for any sands so carried would 

 certainly contain a considerable proportion of tourmaline or schorl 

 grains such as are to be met with in the sands at all levels within 

 the Bovey area that are associated with the clays. There is no 

 mention of such mineral in the detailed descriptions of the Eocene 

 sands of Hampshire, which may be an oversight, but if not, the 

 absence of the mineral must surely necessitate a reconsideration, 

 if not of the origin of the clay, at least of how the clay became 

 disassociated from its native matrix material, to be found in company 

 with other siliceous deposits. 



These considerations arising from the references made to the Bovey 

 clays seem to me to militate against the 'outlier' theory in respect 

 to these deposits, while no such difficulties present themselves in 



