No. 4. About 100 yards from No. 1.
Feet. | ||
|---|---|---|
| Surface | 5 | |
| Blue mud | 5 | |
| Black sand | 3 | |
| Gravel | 3 | |
| Red clay and stones | 34 | |
| Red clay | 44 | |
| Soft blue till | 32 | |
| Hard blue till and stones | 104 | |
| Grey sand not passed through | 22 | |
—— | ||
252 | ||
| Rock-head not reached. | ||
No. 5. About 50 yards north of No. 4.
Feet. | ||
|---|---|---|
| Surface | 6 | |
| Blue mud | 3 | |
| Shell bed | 1 | |
| Channel | 2 | |
| Blue mud | 8 | |
| Channel | 3 | |
| Blue mud and sand | 15 | |
| Red clay and sand | 10 | |
| Red clay | 49 | |
| Blue till and stones | 20 | |
| Sand | 20 | |
| Hard blue till and stones | 24 | |
| Sand | 2 | |
| Hard blue till and stones | 40 | |
| Sand | 7 | |
| Hard blue till | 24 | |
—— | ||
211 | ||
No. 6. Between Heuck and Carron River.
Feet. | ||
|---|---|---|
| Sandy clay | 7 | |
| Mud | 16 | |
| Brown sandy clay and stones | 3 | |
| Mud | 36 | |
| Brown clay | 39 | |
| Blue till and stones | 54 | |
—— | ||
155 | ||
The question arises as to what is the origin of the stratified sands and gravels filling up the buried river channels. Are they of marine or of freshwater origin? Mr. Dugald Bell[285] and Mr. James Geikie[286] are inclined to believe that as far as regards those filling the western channel they are of lacustrine origin; that they were formed in lakes, produced by the damming back of the water resulting from the melting of the ice. I am, however, for the following reasons, inclined to agree with Mr. Bennie’s opinion that they are of marine origin. It will be seen, by a comparison of the journals of the borings made through the deposits in the eastern channel with those in the western, that they are of a similar character; so that, if we suppose those in the western channel to be of freshwater origin, we may from analogy infer the same in reference to the origin of those in the eastern channel. But, as we have already seen, the deposits extend to the Firth of Forth at Grangemouth, where they are met with at a depth of 260 feet below sea-level. Consequently, if we conclude them to be of freshwater origin, we are forced to the assumption, not that the water formed by the melted ice was dammed back, but that the sea itself was dammed back, and that by a wall extending to a depth of not less than two or three hundred feet, so as to allow of a lake being formed in which the deposits might accumulate; assuming, of course, that the absolute level of the land was the same then as it is now.
But as regards the stratified deposits of Grangemouth, we have direct evidence of their marine origin down to the bottom of the Red Clay that immediately overlies the till and its intercalated beds, which on an average is no less than 85 feet, and in some cases 100 feet, below the present surface. From this deposit, Foraminifera, indicating an arctic condition of sea, were determined by Mr. David Robertson. Marine shells were also found in this bed, and along with them the remains of a seal, which was determined by Professor Turner to be of an exceedingly arctic type, thus proving that these deposits were not only marine but glacial.
Direct fossil evidence as to the character of the deposits occupying the western basin, is, however, not so abundant, but this may be owing to the fact that during the sinking of pits, no special attention has been paid to the matter. At Blairdardie, in sinking a pit-shaft through these deposits, shells were found in a bed of sand between two immense masses of boulder clay. The position of this bed will be better understood from the following section of the pit-shaft:—
Feet. | ||
|---|---|---|
| Surface soil | 4½ | |
| Blue clay | 9 | |
| Hard stony clay | 69 | |
| Sand with, a few shells | 3 | |
| Stony clay and boulders | 46½ | |
| Mud and running sand | 11 | |
| Hard clay, boulders, and broken rock | 27 | |
——— | ||
170 | ||