484 



ON THE COAL-FORMATION 



known by the name of silt or sleech, that is, sludge. 

 This soil varies in depth, being from a few feet to 

 nearly 100 feet. About a mile west from the 

 harbour of Alloa, a bore was put down near 90 

 feet ere it reached the rock ; and so soft was this 

 silt, that we accomplished two of these bores in 

 one day. It is to be remarked, however, that the 

 surface above this silt is as good, firm, arable land 

 as any in the district. A great extent of this 

 rich carse has been formed on both sides of the ri- 

 ver, and is of great value. 



There are few or no stones mixed with this 

 soil ; but adjoining the till-district large round 

 blocks of greenstone are found at the surface, 

 which are far detached from any great mass or bed 

 of this kind of rock. 



Below this soil, and close to the rock strata, we 

 in general find a stratum composed of sand mixed 

 with sea-shells ; and the most common kinds of 

 these shells are as follows : 



Ostrea edulis, - Common oyster. 



Mytilus edulis, - musseL 



Cardium edule, - cockle. 



Turbo littoreus, - buckie. 

 Bonax trunculus. 



Patella vulgata, - limpet. 



Of these, the ostrese are large, and to appearance 

 have been of great age when deposited in their 

 present bed, as some of them are more than half 



