T. F. Jamieson — Changes of Level in Glacial Period. 487 



after the existence of the mollusca contained in these beds. Such 

 older shelly strata have been found in the southern part of the Isle 

 of Arran, in Cantyre, in Lanarkshire, and other places. In 

 Ayrshire Mr. John Smith has traced them all over the county and 

 at all heights up to 1061 feet. Now on the east side of Scotland 

 we have several examples of these older shell-beds, but it seems to 

 me we have absolutely none corresponding to the later so-called 

 Clyde beds. So far, however, as I am aware this absence of 

 representatives of the Clyde beds on the east side of Scotland has 

 not hitherto been distinctly asserted by anyone, and no doubt this 

 opinion of mine may be disputed. Nevertheless, I think a due con- 

 sideration should convince anyone who is well acquainted with the 

 shell-beds of the two sides of the country that examples of the later 

 series or so-called Clyde beds really do not exist on the east coast. 

 Nothing like them has turned up on the shores of the Firth of Forth, 

 where, if anywhere, we might expect them to be found. Neither are 

 they to be seen along the Firth of Tay or the Moray Firth. It is 

 true that instances of Arctic shell-beds have been met with at Elie 

 in Fife, and at Errol on the Firth of Tay, but they evidently belong 

 to an earlier submergence, and the Rev. Thos. Brown, who carefully 

 examined these deposits and described them in the Transactions of 

 the Royal Society of Edinburgh for 1867, clearly distinguishes them 

 from the Clyde beds and assigns them, correctly as I think, to- an 

 earlier period. The group of mollusca contained in them comprises 

 fewer species, is of a more intensely Arctic or even circumpolar 

 character, and also indicates a greater depth of water. Moreover, the 

 strata at Elie, Tyrie, and Portobello show evidence of disturbance, 

 having been thrown into convolutions by the action of some powerful 

 force such as the pressure of land-ice, a feature not observable in the 

 later Clyde beds. These were formed apparently when the last great 

 mantle of ice had passed or was just passing away, whereas the 

 older shell-beds belong to an earlier time previous to this glaciation, 

 but subsequent to an older and still greater one. Loch Lomond was 

 at one time a salt-water fiord inhabited by Arctic mollusca belonging 

 to the earlier stage. The shell-beds of that time were then 

 demolished by the later ice coming down the basin, and their 

 remains turned out into the ground beyond. The broken shells may 

 be detected in the railway cuttings between Drymen and Gartness, 

 where I observed them in 1864, both in beds of gravel and in coarse 

 stony mud. Mr. Jack, who afterwards mapped the locality for the 

 Geological Survey, traced a shelly boulder-clay over much of the 

 ground at the south-east corner of the lake, and he attributes the 

 occurrence of the broken shells in the clay to the action of a glacier 

 coming down the bed of the lake and scouring out the marine beds 

 beneath it, an opinion in which I quite agree with him. A great 

 stream of ice had come down Loch Lomond and another down the 

 line of the Forth. These were separated by the mountain ridge 

 running from Ben Lomond towards Balfron, and in the lee of this 

 ridge there are partially stratified masses of clay, sand, and gravel, 

 which seem to have been left there owing to their sheltered position 



