172 PKOCEEDINGS OP THB GEOLOGICAL SOCIETY. [Jan. 11, 



form wide sheets, and range up to 200 and even 300 feet above the 

 sea. 



Now these clay-beds have either never been deposited in the 

 places I refer to, or something has removed them since their deposi- 

 tion. Two or three ways of accounting for this may be suggested : 

 we may suppose that after the marine beds had been laid down in 

 these places they were carried off by the sea itself when the land 

 was emerging from the water, aided perhaps by the action of the 

 rivers ; or we may suppose that, after the land had emerged, the 

 glaciers again took possession of the ground and swept these marine 

 beds out of all the Highland valleys and mountainous tracts ; or, 

 thirdly, it may have been, as I have already hinted, that the sea 

 obtained only a partial possession of the land, owing to the glacier- 

 ice lying in too heavy masses to be floated off" the bottom, and thus 

 preventing the deposition of any marine sediment. 



As a contribution towards the solution of this problem, I shall de- 

 scribe a case I observed last summer in that part of Perthshire 

 which lies to the south-east of Ben Lomond. 



From the south extremity of Loch Lomond there is a tract of low 

 undulating ground stretching north-eastward along the line of the 

 Forth and Clyde Junction Railway into the valley of the Forth near 

 Bucklyvie, and forming a sort of low watershed between that river 

 and the basin of the Clyde. The summit-level of this watershed is 

 only about 220 feet above the sea. Now this tract of land is over- 

 spread with marine clay and sand of the Glacial period. We find in 

 some places (near Balfron, for example) thick beds of red clay, very 

 pure and finely laminated, and used for making bricks and tiles ; 

 in other places this clay alternates with, and passes gradually into, 

 masses of fine soft sand, with occasional beds of gravel. In one of 

 these gravelly seams, at a cutting near Gartness Railway-station, I 

 found remains of sea-shells, generally much broken and water-worn, 

 but some of the smaller ones entire. Of these I collected fourteen 

 species (see Appendix, No. 4) of the same kinds and of the same 

 northern character as those met with in the Clyde beds at Paisley 

 and elsewhere. The position of this shelly gravel, as I learn from 

 the levels of the railway, is about 120 feet above the sea. Stones 

 and boulders are not uncommon in some of these marine beds, and 

 much of the clay is of rather coarse quality. 



Now when we descend into the valley of the Forth and go to 

 the Loch of Monteith, which is only a few mUes from Bucklyvie, and 

 at a considerably lower level than the shelly gravel at Gartness, this 

 red clay and sand is no longer to be seen, and we find ourselves 

 among large abrupt mounds of gravel and rough stony debris, full of 

 heavy boulders, and piled together in a confused manner without 

 any regular stratification — in short, having all the appearance of 

 glacier-moraines. This picturesque little lake, in fact, seems to be 

 formed by a great heap of moraine -debris, which stretches across the 

 valley of the Forth as if it had been formed by a glacier coming 

 down from the flanks of Ben Lomond and Ben Yenue ; a transverse 

 barrier has thus been produced which obstructs the drainage. The 



