POST-TERTIARY FOSSILIEEROUS DEPOSITS. 85 



II. — A strongly marJeed series of Post-glacial deposits belongs to the most recent period 

 of the depression of the land. 



These beds when fossiliferous contain precisely the same fauna as that now occupying 

 British waters. They are, however, sometimes distinguished {a) by a general grouping 

 of species in slightly different proportions from those now prevalent in the waters of 

 the special locality, and {h) by the rarity or absence in the immediately neighbouring 

 waters of a species abundant in the fossil bed. 



The deposits, which may be classed together as belonging to the close of the last 

 period of the depression of the land, range from a little above the sea-level to a height of 

 about forty feet, and may be described as raised beaches and estuarine beds. 



A. — Estuarine muds compose the Carse Lands of Scotland, and are largely developed 

 in the Firth of Tay and the Firth of Forth. The mud is in no way stony, but exceedingly 

 fine and smooth, and has not been disturbed since its first deposition. 



A series of bores (investigated by Mr. Croll and Mr. J. Binnie^) " reveal the existence 

 of a deep trough or channel, running from the Clyde \ alley, near Bowling, up to and 

 through the haugh of Belmore, the valley of the Kelvin, and round by the south-east end 

 of the Campsie Hills into the valley of the Forth by Grangemouth and one of these will 

 clearly show the general position of the estuarine mud.^ 



Bore near Skinflats, Grangemouth, twelve feet above sea-level.* 



1. 



Surface sand . . . . . 



6 feet. 



2. 



Soft mud with shells [estuarine, Ostrea edulis very large — 







many recent species] . . . . 



11 



3. 



Blue mud and sand (hard) . . . . 



3 



4. 



Channel (rough gravel) . . . . 



3 



5. 



Fine sand [shell fragments] 



8 



6. 



Running sand (red and fine) 



17 



7. 



Red clay . . . . . 



30 



8. 



Soft till [Boulder Clay] . . . . 



36 



9. 



Sand (pure) . . . . . 



2 



10. 



Soft till [Boulder Clay and sand] 



17 



11. 



Gravel . . 



8 



12. 



Hard blue till [Boulder Clay] 



14 







155 



1 'Trans. Geol. Soc. of Glasgow,' vol. iii, page 141. 



2 With respect to this channel between the Forth and Clyde it must be noted that when the land stood 

 higher the trap-dyke which crosses the Clyde near Dalmuir would have assisted in forming the deep portions 

 of the trough into a lake such as Loch Lomond now is, with its bar at Balloch. 



' Ibid., p. 144. 



