OLD RED SANDSTONE OF WESTERN EUROPE. 349 
the development of the formation on either side of the Atlantic will show 
that neither in depth of strata nor in paleontological interest is the European 
Old Red Sandstone so depauperated as has been supposed, and I hope that the 
present memoir may be so far useful in affording materials for such a comparison. 
An essentially lacustrine series of deposits, besides being originally of limited 
extent, necessarily runs great risk of being largely removed by denudation, or 
of being buried and concealed under later, and especially marine, accumulations. 
The Old Red Sandstone, even at the first developed only locally, and subsequently 
overspread successively by younger geological formations, now occupies a com- 
paratively small area in Western and Northern Europe. From the south-west 
of Ireland it may be followed through the rest of Britain as far as the distant 
Shetland Islands, and across the intervening tract of sea into the south-west of 
and south of Scandinavia; while far to the east in Russia it reappears in almost 
horizontal strata, which cover a space considerably larger than the area of the 
British Islands. 
Inno part of its European distribution does the Old Red Sandstone attain the 
thickness and variety which it presents in Scotland. In that country its most 
characteristic features—sandstones, flagstones, conglomerates, lavas, tufts, fishes, 
crustaceans, and plants—are so admirably preserved, that the Scottish Old Red 
Sandstone may with reason be described as a type for the system. Numerous 
sections on the sea-coasts, in inland ravines, and river courses, as well as on 
bare hillsides, allow of the thorough investigation of almost every strati- 
graphical detail. For many years its abundant’ fossil treasures have been 
sedulously gathered by many enthusiastic collectors. But notwithstanding the 
numerous memoirs which have from time to time appeared, much remains to 
be done before our knowledge of the history of the Old Red Sandstone in Scot- 
land and the surrounding regions is brought up to the same fulness as our 
acquaintance with that of the Carboniferous system which followed it. Over 
large tracts of country the stratigraphical relations of the various portions of 
the system have never been determined. The order of succession in the Old 
Red Sandstone on the north side of the Grampian mountains, for example, has 
never yet been adequately worked out. Yet this part of the subject is of 
paramount consequence in any attempt to unravel the chronology of events of 
which the strata of the Old Red Sandstone are the records. 
I propose in the present memoir to attempt to trace a series of changes if 
the physical geography of Western Europe, which took place between the close 
of the Upper Silurian and the commencement of the Carboniferous period. 
As this history must be based upon a rigorous examination and comparison 
of sections in different districts, I shall be under the necessity of presenting 
hitherto unpublished observations in greater detail than I could have wished. 
After many years devoted specially to the investigation of the Old Red 
VOL. XXVIII. PART II. 4¥Y 
