6*92 
PROFESSOR PRESTWICH ON THE ORIGIN 
found except close to the sea-level (the exact age of these seems uncertain); though 
in the islands of the Northern Hebrides there are shelly clays as high as 175 feet.* 
We are not, however, to conclude on the negative evidence that the sea reached no 
higher than indicated by these fossiliferous deposits. Some of the sands and gravels 
at higher levels may be attributed to marine action. Even on the east coast fossili¬ 
ferous beds are the exception, and Mr. Jamieson has reasonable grounds for saying 
that “we are not entitled to say that the submergence reached no higher than 500 feet 
merely because marine fossils have not been discovered at great heights. ”+ 
The higher Baised Beaches on the west coast afford corroborative evidence. No 
shells have been found in them, but this might be owing to the exposed nature of the 
coast or to the shells having been dissolved out. Their horizontal lines, and the per¬ 
fectly well rolled large pebbles of which they are formed, leave no doubt of their origin. 
The lower 10 feet and possibly the 40 feet Beaches are of more recent date, and I do not 
now refer to them but to the higher terraces noticed by Captain Vetch, j Admiral 
Bedford, § the Duke of Argyll, || and Mr. J. F. Campbell, IT which are in all probability 
of glacial age, and may belong to this intermediate period of submergence. They are 
very distinct on the west coast of Jura, where the Duke of Argyll ascertained their 
heights by aneroid barometer to be respectively 50, 75, and 125 feet above present sea 
level, while some in the distance appeared to be higher. Further north he thinks they 
have been traced to the level of 160 feet. 
Assuming the submergence in the Highland district to have been only 400 to 500 
feet, if we add to this the greater height of the land at the period of previous glaciation, 
it would, on Dr. J. Geikie’s estimate of about 600 feet, or of my own of 1,200 feet or 
more, establish a difference of not less than 1,000, and possibly of more than 2,000 feet, 
in the height of this part of Scotland between the two periods we are considering. 
This difference of level would produce a two-fold effect upon the climate : 1st, that 
resulting from altitude, which allowing 1° Fahr. for every 300 feet of elevation, would be 
equal to a change in mean temperature of from 3° to 6° Fahr. ; 2nd, that caused by the 
conversion of a continental area into an archipelago. This last would have a much 
more sensible effect on the temperature, for the Highlands of Scotland became, in con¬ 
sequence of this subsidence, surrounded by an open sea, with only the higher peaks of 
Ireland, Wales, and the North of England above the waters, so that the warm currents 
of the Atlantic reached the foot of the Highland mountains, and penetrated deep into 
the land—a result which could not have failed to bring about a very important amelio¬ 
ration of climate, possibly to the extent of from 9° to 10° Fahr., or may be more.** 
* J. Geikie, Quart. Jonrn. Geol. Soc., vol. xxxiv., p. 863. 
f “ Last Changes in Scotland,” Quart. Journ. Geol. Soc., vol. xxi., p. 177. 
| Trans. Geol. Soc., 2nd ser., vol. i., p. 416. 
§ Quart. Journ. Geol. Soc., vol. ii., p. 577, and vol. xii., p. 167. 
|| Trans. Brit. Association for 1866, p. 86. 
Op. cit., p. 9. 
** The effect would be somewhat analogous to the removal of the seaboard from the west to the east of 
