200 H. B. Woodivanl and J. R. Blake— 



of sun-cracks, pseudomorphous crystals of rock-salt, ripple-marks, 

 sands and conglomerates. 



Some writers^ have pointed to the occurrence of perforations by 

 boring molluscs in the top beds of the White Lias. During the past 

 four years we have looked in vain for any such evidence. There are 

 certainly curious hollows sometimes apparent in these beds, but none 

 that we have observed could be referred with certainty to the action 

 of Pholas or any other marine mollusc. Nor have any traces (so far 

 as we are aware) of any marine boring mollusc been detected 

 in these beds. Pholas is not even recorded from the Lias of this 

 country.^ 



There seem to be two kinds of perforations. The one in the form 

 of hollows in the stone, evidently produced after the consolidation 

 of the rock. But we have noticed that wherever these occurred it 

 was either where the beds were denuded of the Lower Lias, and thus 

 exposed at the surface, or it was on the faces of joints. They are 

 clearly due to atmospheric influences ; possibly snails may have done 

 something, but sufficient evidence of the boring power of these 

 animals has not yet been brought forward. Some few holes, as Mr. 

 Moore tells us, are due to the weathering out of Corals. 



The other kind of perforation is that which occurs in the upper 

 beds of the White Lias at Curry Eivell, near Taunton. Messrs. 

 Bristow and Etheridge have obtained some very fine specimens 

 showing tubular perforations extending two or three, and sometimes 

 nearly six inches, into the stone. They are deposited in the Museum 

 at Jermyn Street. The nature of these perforations indicates that 

 they were formed contemporaneously with the sediment now con- 

 solidated, that is to say, that they were the burrows of some marine 

 animal in the soft calcareous mud of the Eheetic period. Mr. 

 Etheridge is inclined to refer them to an Annelid, or possibly to 

 Lithodomus. It is not, however, probable (the stratigraphical 

 evidence so strongly forbidding such a notion) that the upper beds 

 of the White Lias were consolidated previously to the deposition of 

 the Lower Lias ; so that we could not expect to find evidences of 

 perforations by any lithodomous mollusca of that period. 



Sometimes the upper surface of the Sun-bed or Jew-stone, where 

 it is exposed, presents a striated appearance, being crossed in all 

 directions by fine grooves. It is difficult to account for this ; but the 

 notion originally suggested by the Eev. J. Sutcliffe,^ that such 

 striations on limestones were originally sun-cracks, seems a plausible 

 theory. Subsequent pluvial action has done much to modify and 

 enlarge them. 



The Cotham Marble, which occurs at the base of the White Lias, 

 and frequently the Sun-bed, have an irregular corrugated surface, 

 which, as Conybeare* remarks, "sometimes represent the interlacings 



1 Amongst whom Moore, Quart. Journ. Geol. Soc, vol. xxiii., p. 496. 



2 Tate, Census of the Marine Invertebrate Fauna of the Lias, Geol. Mag., 

 Vol. VIII., p. 4. 



3 A short Introduction to the Study of Geology, 1817, p. 21. 

 * Geology of England and "Wales, p. 264. 



