Mackintosh — Railway Geology in Devon. 395 



the sea covered the north-west part of the present Bovey plain to a 

 height of at least 14:0 feet ; and, as the denudation of the body of the 

 Bovey formation must have occurred before the deposition of the 

 "head," it is probable that this deposition took place under a very 

 considerable depth of salt water. Both events, the deposition of 

 the "head," and the perforation of the limestone rocks, may have 

 occurred dui'ing the cold period. Dr. Heer has rendered this certain 

 so far as the "head" is concerned. The immense mass of clay and 

 sand composing the body of the formation could not have been carried 

 from Dartmoor by a river of a size equal to any watershed dependent 

 on the present configuration of the grou.nd ; and the same remark 

 applies to the timber which supplied the beds of lignite, and which 

 Dr. Heer admits could not have principally come from the shores of 

 a lake. The waves of a lake only about two miles in average breadth 

 could have done little to distribute sand, clay, and heavy timber. The 

 layers of the Bovey formation are not arranged (even in the same 

 beds) according to specific gravity, as would have been more or less 

 the case in the tranquil waters of a lake. The beds of sand thin out 

 in a way indicating denudation by currents. Thus the thick middle 

 bed of sand, in thinning out eastwards, in places exhibits an abrupt 

 termination of its subordinate beds. Fragments of lignite, which 

 look as if they had been denuded out of older lignite beds by cur- 

 rents, occur in the clay beds. In the thick bed of sand there are 

 intercalations of clay and differently coloured sands, which point to 

 a to-and-fro action, such as is now producing similar phenomena in 

 tidal zones, and probably at greater depths in the sea. Approximations 

 to false-bedding occur in the above bed of sand as well as in some 

 parts of the " head." Nothing but currents denuding and re- 

 depositing, and at intervals changing their direction, during a long 

 lapse of time, would seem to offer a sufficient explanation of these and 

 other phenomena connected with the Bovey formation. On many 

 coasts, and in bays and estuaries, in recent times, currents have 

 brought from a distance and deposited immense quantities of pm-e 

 sand or clay, sometimes alternating, and' this irrespective of the 

 nature of the immediately adjacent rocks. In lakes no such de- 

 posits, distinct from coast materials, can accumulate much beyond 

 the delta or sides of traversing rivers ; and it is improbable that the 

 surface of the supposed Bovey lake ever reached the level of the 

 granite on the west and north, from which the Bovey sands and 

 clays are believed to have been mainly derived. The great masses 

 of heavy timber, now compressed into lignite, in the lower part of 

 the Bovey formation, would seem to imply, as an efficient cause, a 

 neighbouring forest-area gTadually, or paroxysmally, subsiding under 

 the encroaching influence of oceanic currents. 



Old sea-bed — Slate and Igneous Bodes. — That this district has been 

 at least once submerged to a depth of not less than 140 or 200 feet 

 below its present level, would appear not only from the Torquay 

 Pholas-hormgs, but from the discovery of an extensive bed of boulder- 

 drift very lately exposed by railway cuttings to the north-west of 

 Bovey. It may at one time have covered a continuous slope, re- 



