Mr Smith on the Changes of the Level of the Sea, 381 



We must be cautious, therefore, in concluding that alluvial 

 beds in which we do not find such remains, are fresh-water 

 ones ; and, of course, equally so in deciding on their marine ori- 

 gin, till confirmed by the presence of their appropriate remains. 



These deposits are much more extensive, both as to the 

 amount of change of level and superficial extent, than has been 

 generally supposed. We have conclusive evidence that the 

 whole of the British islands have, at periods which, geologically 

 speaking, are by no means remote, been subjected to changes 

 both of depression and elevation. The submarine forests which 

 have been observed on so many parts of our coasts, are proofs 

 of the former kind of changes, whilst those of elevation are evi- 

 denced by raised beaches, sea-worn cliffs and caves, stratified 

 beds of sand, gravel, and clay, and, above all, by the marine 

 exuviae which they contain. 



The deposits thus formed must, in Scotland at least, be in- 

 tercalated between the two first groups in Mr De la Beche's clas- 

 sification of rocks, viz., the modern group and the erratic block 

 group. We infer that they are posterior to the latter, from 

 their superposition, and that they do not belong to the former, 

 from the absence of the remains of man or of works of art. 

 The erratic block bed, which has also been termed diluvium, 

 has in Scotland received the provincial name of Till. It is very 

 accurately described by Mr Bald,* under the name of the old 

 alluvial cover, in his paper on the coal formation of Clackman- 

 nanshire. It generally consists of stiff unstratified clay and 

 gravel, confusedly mixed with water-worn masses, and also with 

 angular fragments of sandstone, shale, and coal, which have 

 not suffered from attrition, although comparatively soft in their 

 structure. Organic remains are excessively rare in it. Mr 

 Bald, who remarked this, afterwards found the tusk of an ele- 

 phant embedded in it in the excavation of the Union Canal ; 

 but, unwilling to draw an important inference from a solitary 

 fact, he supposed it might have been placed in the situation in 

 which it was found, from some accidental cause. Since that 

 time, however, elephants' bones and tusks have been found 

 near Kilmarnock, and at Kilmaurs, in Ayrshire. I am assured 



* Wern. Mem. vol. i. p. 481 ; vol. iii. p. 126. 

 VOL. XXV. NO. L. OCTOBER 1838. C C 



