ON CAVES. 5 



rocky shore, or filled with heaped-up pebbles, if it opened on to 

 a shingle beach. By its form and by its contents we could 

 generally make a shrewd guess whether it was a sea-cave or 

 not. We should ask whether the parts where the cave 

 expands are those on which the sea would act with greatest 

 force and efficiency, or whether the shape could be better 

 explained by reference to torrents coming in the other 

 way. We should examine the contents to see whether in 

 their character or arrangement they indicated the action of 

 the in-rushing water, or whether they are such as could never 

 have survived the scour of tidal and wind-driven waves. 

 When we have to inquire into the origin of caves in inland 

 cliffs and on mountain-sides, now far above the sea, where 

 many of the traces above-described may have been long 

 removed by denudation, there are further tests to be applied. 

 There we should have regard to their manner of occurrence 

 and their place in the physical geography of the neighbour- 

 hood. A sea-cave does not necessarily, or even commonly 

 occur in the line of drainage from the uplands, but in the 

 higher cliffs and headlands between the valleys that run down 

 to the sea. Whereas the caves due to subterranean water- 

 courses lie in the lines of drainage ; and the caves due to 

 sub-aerial waste coincide in distribution with the outcrop of 

 the beds that readily lend themselves to that kind of 

 weathering. 



Moreover, allowing for the possibility of unequal elevation 

 of different parts of a coast-line, we can still generally find 

 sufficient evidence to show whether the rock in which the 

 cave occurs forms part of an old sea-cliff or of an escarpment.* 



We must remember also that during the formation of a 

 sea-cave the base of the cliff is being swept by the sea. 

 Sometimes an inland stream washes the base of a rock in 

 which a watercourse cave has its outfall, but generally in the 

 case of inland-formed caves a vast mass of talus is being 

 formed along the base of the cliff in which the cave occurs. 

 The scour of floods may keep the mouth open, but as the 

 water is being drained off to other ^and lower levels, this sweep- 

 ing of the cave mouth ceases, and the cave deposits show 

 interbedded fallen rock and transported earth and stones, and 

 often the remains of animals. 



As a general statement we may say that a typical sea-cave, 

 runs into a cliff which rises vertically from the level of the 



* Cf. Whitaker, Q.J.G.S. vol. xxiii. c. 186, p. 265. Geol Mag. vol. iv. 

 1867, pp. 457, 443. 



