70 THE CRUISE OF THE BETSEY ; OR, 



from which streams descended, sweeping with them, to the 

 marine depths, productions, animal and vegetable, of the land, 

 But it is less easy to conceive, that in that sound, the area 

 covered by the ocean one year should have been covered by 

 a fresh-water lake in perhaps the next, and then by the ocean 

 again a few years after. And yet among the Oolitic deposits 

 of the Hebrides evidence seems to exist that changes of this 

 nature actually took place. I am not inclined to found much 

 on the apparently fresh-water character of the bituminous 

 shales of Eigg ; the embedded fossils are all too obscure to be 

 admitted in evidence : but there can exist no doubt, that 

 fresh-water, or at least estuary formations, do occur among 

 the marine Oolites of the Hebrides. Sir R. Murchison, one 

 of the most cautious, as he is certainly one of the most dis- 

 tinguished, of living geologists, found in a northern district 

 of Sky e, in 1826, a deposit containing Cyclas, Paludina, Ne- 

 ritina, all shells of unequivocally fresh-water origin, which 

 must have been formed, he concludes, in either a lake or es- 

 tuary. What had been sea at one period had been estuary 

 or lake at another. In every case, however, in which these 

 intercalated deposits are restricted to single strata of no great 

 thickness, it is perhaps safer to refer their formation to the 

 agency of temporary land-floods, than to that of violent changes 

 of level, now elevating and now depressing the surface. 

 There occur, for instance, among the marine Oolites of Brora, 

 the discovery of Mr Robertson of Inverugie, two strata 

 containing fresh-water fossils in abundance ; but the one stra- 

 tum is little more than an inch in thickness, the other little 

 more than a foot ; and it seems considerably more probable, 

 that such deposits should have owed their existence to extra- 

 ordinary land-floods, like those which in 1829 devastated the 

 province of Moray, and covered over whole miles of marine 

 beach with the spoils of land and river, than that a sea-bottom 

 should have been elevated, for their production, into a fresh- 



