1849.] CUMMING ON THE TERTIARIES OF THE MORAY FIRTH. 15 



spreads out into a fine terrace rising from a cliff of 90 feet fronting 

 the river Ness, to about 115 feet a mile and a half inland, in the 

 neighbourhood of Drakies. We have it thence spreading out east- 

 ward by Culloden House into the extensive plains of Nairn and 

 Morayshire. I can hardly help regarding it as identical in age with 

 the great drift-gravel platform which I have mentioned as in the Isle 

 of Man occupying a large space in the southern and central valleys 

 of the island. It seems to me to be a fragment of that sea-bottom, 

 whicb, when upheaved, united the British Isles with each other and 

 with the continent of Europe, and which has not since been sub- 

 merged, but gradually eaten away by oceanic currents acting through 

 a very lengthened period. The erosion has proceeded to an extent 

 greater than that indicated by the present outline of our coasts, 

 having been stopped by another elevatory movement of the land. 

 This appears to be indicated by the cliffs of this drift-gravel, often 

 far inland, but almost always found at the opening of estuaries, or 

 where arms of the sea run up into the country, having at their bases 

 extensive raised beaches of a more recent period. We have such a 

 lower sea-beach very distinctly developed along the Moray Firth. In 

 the immediate neighbourhood of Inverness it spreads out into a terrace 

 of many thousand acres, and the lower town is built upon it at an ele- 

 vation of from twelve to fifteen feet above the present high-water mark. 



It is evident therefore that when the depression of the land was to 

 the extent of 100 feet and upwards compared with the present sea- 

 level, the entire Caledonian Valley formed a narrow strait insulating all 

 the counties to the north of it. As the land rose, the passage of waters 

 through this strait would be interrupted, and other circumstances 

 would operate in the formation of terraces at lower levels, such as the 

 draining of the lochs and the deposit of alluvial deltas at the mouths 

 of rivers. In fact, as soon as the communication was cut off in this 

 direction between the seas of the eastern and western sides of Scot- 

 land, an extended plateau was originated whose superior limit would 

 be coincident with the present summit-level of the Caledonian Canal, 

 and it would immediately become subject to a variety of destructive 

 agents, which would leave it in patches on each side of narrow valleys, 

 or cut up by river-courses in the more open country. 



Hence, again, if we consider the depression of the land to have 

 been to the extent of 1200 instead of 100 feet, and then that gra- 

 dually the land rose again, we have plainly all the conditions requisite 

 for the formation of such still more elevated terraces as those which 

 occur in Glen Roy. 



And hence again, inversely, we may regard such terraces as these as 

 gauges of the depth of submergence to which our Scottish mountains 

 were at least submitted. 



An important inquiry still remains, viz. to what are we to attribute 

 the great current which seems, through so long a period, to have been 

 flowing over the face of the Highlands in an easterly direction ? The 

 answer will probably involve the phsenomena of the distribution of 

 erratics in other portions of the British Isles. 



Professor Forbes has made a remark, which appears to me to bear 

 upon this question. ** The phsenomena of the glacial formations," he 



