﻿1851.] 



DUKE OF ARGYLL ON ARDTUN LEAF-BEDS. 



95 



2 feet thick; and the lower portion of it is not so much mineral 

 matter with organic impressions as a compressed mass of leaves, not 

 a few of which, when the layers are partly divided, seem still to retain 

 the damp obscure colours of vegetable decay. The composition of 

 the bed becomes harder, as it passes upward, where there is more and 

 more mineral matter, with fewer impressions of plants. These are 

 still, however, frequent, preserving in large and small leaves the most 

 delicate tracery of the skeleton. Some few impressions of twigs are 

 found even above the limits of the bed, and here and there mark the 

 lower portions of the superincumbent tuff. 



5. The fifth bed is a second band of tuff, similar in composition to 

 the one above described, but somewhat thicker. Owing, however, to 

 its dipping under the sloping base of the ravine, less of its course is 

 visible than of the one above. 



6. The sixth bed is a seam of what may be best described as baked 

 clay or very fine mud. It is very brittle, but without any particular 

 form of fracture. From its general appearance and relative position 

 among the beds, it at once suggests itself to be a third leaf-bed. 

 Accordingly, after some search, a few impressions were obtained of 

 leaves apparently similar in character to those found in the superior 

 deposits. But the nature of the material prevents more than mere 

 fragments being obtained. 



7. Below this third and last leaf-bed the cliff is composed of a dark 

 amorphous basalt. Like most of the traps and basalts of the district, 

 it is of an amygdaloidal structure, the cavities being filled with various 

 mineral crystals. On the surfaces exposed to the action of the air 

 and sea-spray these have decayed out, and the empty holes give here 

 and there a honey-combed appearance to the rock. 



8. Lastly, the cliff ends in beautifully columnar basalt, dipping 

 into the sea. I have not ascertained the soundings nor the nature of 

 the bottom, and consequently am unable to say what may be the 

 height of the columns. They may be seen, however, to a consider- 

 able depth in the clear waters of that sea. They are sometimes per- 

 pendicular, sometimes bent in various directions ; a common disposi- 

 tion here being, as at Staffa, a gentle outward curve, as if bending 

 under the weight of the superincumbent cliff*. 



The point, at which the ravine exhibits a section of these beds, is 

 that at which the headland reaches its highest elevation. To the 

 W. and E. it declines in height ; but the beds containing the vege- 

 table impressions can be traced for a considerable distance along the 

 sea-face ; and excellent specimens have been obtained from the second 

 leaf-bed about 100 yards farther to the E. It has been mentioned 

 that the beds dip gently towards the S. ; that is, in a direction nearly 

 parallel to the line of Loch Laigh. The surface of the headland of 

 Ardtun follows the same slope ; so that at the head of Loch Laigh — 

 that is, in the course of about a mile along the line of dip— the land 

 is but slightly elevated above the level of the sea, and it is remark- 

 able, that at both sides of this headland — upon the shore of Loch 

 Scridden and that of Loch Laigh — a seam of coal has been found 



* Since writing the above, I have received from Mr. M'Quarrie a measurement 



