:"58-4 ON THE FAUNA AND BOTTOM-DEPOSITS NEAR THE 30-FM. LINE 



"The presence of the Trias is not surprising. The probable existence of 

 submarine Trias between the Lizard and Plymouth had already been 

 suggested by E. N. Worth, who, in 1886, reported the existence of a sub- 

 marine Triassic outlier, having its centre about ten miles south-east of the 

 Lizard. (Quart. Join: Geol. Soc, Aug., 1886.) 



" But although not altogether unexpected, this Trias of the Eddystone 

 neighbourhood is now reported for the first time, and deserves more detailed 

 and lengthy description than would be appropriate to the objects of the 

 present investigation. For present purposes it will be sufficient to state that 

 the nearest shore exposures of rocks of similar formation occur at Oddicoml^e 

 Beach, St. Mary Church, again at a point immediately to the west of the Bolt, 

 and lastly, on either shore of Plymouth Sound, in Cawsand Bay and to the 

 south of Bovisand respectively. 



"The presence of the iron of the Trias has apparently had its effect on the 

 foraminifera, for some of the Miliolina especially present an unusually 

 ferruginous appearance. 



"Among the Eddystone gravels were found scattered fragments of 

 amorphous silica, insufficient in number or weight to affect numerical results. 

 These were mostly regarded as Triassic before the Bolt examples had been 

 examined. Such an identification was justified by the known existence of 

 veins of calcedony in the submarine Trias off the Lizard. Their absolute 

 identification is still problematic. Not so, however, with the flint gravel 

 from the Bolt district. This, although much affected by the solvent action of 

 the sea-water, is still recognisable as flint, and possibly more exact information 

 may on further examination be derived from some of the apparent fossils 

 which have survived the solvent action of the water. It is interesting to note 

 the extent to which this solution has been carried. The outside of practically 

 every flint pebble has been converted by it into a microscopic honeycomb, 

 and only the larger fragments have any core of unaffected silica remaining. 

 The crystalline quartz grains of the Trias, on the other hand, have resisted 

 the chemical action of the water. 



"The sands are interesting as giving evidence of the relative degree to 

 which Avave action has affected the sea-bottom. It may seem a truism to 

 suggest that a fine -grade sample may owe its fineness of textures either to 

 the presence of a large quantity of fine sand or to the absence of all but a 

 small proportion of coarser gravel. The two causes are, however, quite 

 distinct, and cither may act alone or both in conjunction. 



" The dredgings in the Eddystone neighbourhood are not perhaps so many 

 or so scattered as might be desired for this discussion, the objective having 

 been rather zoological than geological. None the less, it is interesting to note 

 the relative positions of the fine textures an<l the coarse textures. With one 

 exception the fine textures occur at some considerable distance from the reef, 

 while the coarse textures are clustered around the reef or around the Hand 

 Deep.s. The exception as to a fine texture occurring near the reef is in the 

 case of dredging 89J>, taken from the centre of the channel between the Hand 

 Deeps and the Eddystone reef. 



