3Ik. Fergusos on a Marine Deposit containing Shells. 151 



sea level must have been stationary at tliis height, and if we may judge 

 of its duration from the relative size of the ancient terraces with those 

 now forming, it must have exceeded the recent period, of which '2000 

 years is but a part, by an immense amount; but this is but one of the 

 epochs in the history of this formation : between the great terrace and the 

 sea, several subordinate ones and beaches have been observed, each of 

 them marking long continued periods of repose, whilst a sudden deepen- 

 ing two or three fathoms below low water mark is probably caused by 

 another line of terraces now covered by the sea." 



The following table of the classification of the different formations of 

 this, the pleistocene or glacial period of geology, is constructed from Mr. 

 Smith's paper, and will help us to form an idea of the extent of time 

 necessary for its production : — 



1. Elevated marine beds. Ancient beaches. 



2. Submarine forests. 



3. Alluvial beds, most likely marine, but affording as yet no organic 

 remains. 



4. Upper diluvium or till, the most recent deposit of the till. 



5. Marine beds in the till affording shells, at Airdrie. 



6. Lower diluvium, till, or boulder clay. 



7. Stratified alluvium, consisting of sand, gravel, and clay, without 

 organic remains, resting in this district immediately upon the u^iper mem- 

 bers of the carboniferous system. 



I have divided the diluvium or till into two members, as certain recent 

 observations, lately laid by Mr. Smith before the Geological Society, have 

 shown it to have been deposited at two periods, with quiet water inter- 

 vening, and this also adds indefinitely to the already almost boundless 

 extent of time required for the development of these beds. 



Without entering into any of Mr. Chambers's conclusions as to uni- 

 formity in the oscillations of level of the sea and land, or the vexed ques- 

 tion as to whether it is the land that has risen or the sea that has fallen, 

 we may conclude with him, that there was a time when "the Frith of 

 Clyde was a sea several miles wide at Glasgow, covering the site of the 

 lower districts of the city, and receiving the waters of the river not lower 

 than Bothwell Bridge," And we may imagine that at the time when 

 these beds of sands were being laid down, where I have described them 

 in the hollow of Sauchiehall-Street, the waters of this noble estuary eddied 

 around the various eminences which yet mark the physical geography of 

 Glasgow. Garnethill would stand out conspicuously, separated by a 

 narrow and not deep channel from Blythswood-hill. A broader and deeper 

 current would flow betwixt it and the hill where Port-Dundas now stands, 

 finding its way into the main channel farther westward, while to tho 

 south the wide expanse of water would sweep onward, with perhaps an 

 islet here and there, towards the Cathkin and other southern hills, pre- 

 senting more the appearance of a landlocked bay or inland sea, than an 

 estuary. But on the remote antiquity of this era who shall speculate ? 



Vol. III._No. 3. 2 



