202 The Scottish Naturalist. 



will find that, comparatively short though the period be that 

 separates that age from the present, it was yet crowded with changes 

 and vicissitudes. Many of these have left their marks upon the 

 surface of the land, while others are to be read in the present dis- 

 tribution of our plants and animals. And I cannot but believe 

 that when these living fossils (if I may so call them) come to be 

 more carefully studied in their various relations, we shall know 

 much more than we do at present concerning some of the more 

 recent climatic and geographical changes of North-Western Europe. 



Of the flora and fauna which existed in Scotland in pre-glacial 

 times, no unequivocal relic has come down to us ; but we may 

 infer from what is known of the pre-glacial plants and animals of 

 England and the Continent that the assemblage of species here 

 was, in a general way, much the same as at present. During inter- 

 glacial times a somewhat similar flora and fauna characterised our 

 land; but the last ice-sheet which overflowed Scotland made a 

 clean sweep of every living thing, so that the history of the present 

 flora and fauna dates only from the latter end of the glacial period. 

 The geographical and climatic conditions of late glacial and post- 

 glacial times, so far as I have been able to read them, can be very 

 shortly summed up. They had unquestionably an overpowering 

 influence in producing the present distribution of species, and I 

 have long been of opinion that when naturalists shall have exhaust- 

 ively studied our flora and fauna, they will be able to throw much 

 more light upon the succession of changes to which I refer. 



The gradual disappearance of glacial conditions in our area was 

 accompanied and followed by some degree of submergence ; so 

 that Middle Scotland in late glacial times stood at a lower level 

 than it does now, by ioo feet or thereabout. This was the 

 period during which the ioo feet terrace of our great firths was 

 formed, of which distinct traces occur in the Firth of Tay, 

 in the valley of the Eden, and in the Firth of Forth. Followed 

 inland, this terrace passes into tumultuous glacial gravel and 

 sand — and sheets of sand loam, and clay — deposits which are 

 associated, as in Strathmore, with morainic hills and ridges of sand 

 and gravel. Scotland at this period must have presented a dreary 

 aspect. Perennial snows and ice-fields covered all our mountain- 

 regions, down the valleys of which flowed great glaciers that 

 reached the sea-level. The Ochils and the Sidlaws were likewise 

 covered with snow; and in summertime heavy torrents descended 



