96 
THE GEOLOGIST. 
after many ages had elapsed aud hundreds of years had passed away, 
an immense series of strata was elaborated, which extended continu- 
ously over the site of the Pentlands. The same waters under which 
was laid down the ash of the Dry Dam, and which held in solution 
the substances which fill the amygdaloidal cavities of the greenstones 
and felstones above it, also deposited above these rocks an enormous 
series of beds, 3000 ft. thick at least, of sandstone, shale, and lime- 
stone, the edges of which are seen on the beach eastwards from 
Portobello. and at East Cairn Hill on the Pentlands, at a height of 
1839 ft. above the level of the sea, i. e. 1000 fc. above Arthur's Seat. 
These rocks also extend northwards into Fife. This is represented 
in the accompanying diagram. 
It is perfectly evident then, from what has been already said, that 
Lower Carboniferous strata muSt have been elaborated far above the 
present altitude of Arthur's Seat, and that their area extended for a 
considerable distance on all sides, overlying the whole ridge of the 
Pentlands. It is also pretty clear, both from the horizontal beds of 
sandstone on the summit of East Cairn Hill, and from the state of' 
the case generally, that these strata were at first laid down in a hori- 
zontal position, or at all events very nearly so. 
Now, the nej^f stage through which these rocks passed is easily de- 
termined. An uplieavinq movement must have taken place, by which 
the whole beds of the hill, already alluded to as forming the eastern 
part, on to the centre of the Musselburgh basin, were raised into the 
inclined position in which we now find them. If evidence of this up- 
heaval is wanted, we have only to point to St. Leonard's Craig, Salis- 
bury Craigs,with tiie two dykes cutting through them, and the Dasses, 
the only intrusive traps of the hill, and all found on the western side. 
The eff'ects of this upheaval are well displayed at Salisbury Craigs, 
where the beds have an easterly dip, being raised on the west and 
depressed on the east, and where both the sandstone and the green- 
stone are altered in colour and texture at the point of contact. In- 
deed, nothing shows the intrusive character of this trap more clearly 
than the seam of shale to be seen at the south end of the Craigs, very 
much hardened and broken, lying completely enveloped in the green- 
stone. After this eruption, then, the rocks of the hill would present 
somewhat the appearance given in the accompanying diagram, PI. Y. 
But this is not the present aspect of the hill ; Carboniferous strata 
no longer conceal the trap-rocks from view. How, then, have they 
disappeared ? What has become of them? The answer is, denuda- 
tion must have taken place. Now I think it is a fact which can be 
easily demonstrated, that Arthur's Seat has been subjected to denu- 
dation at two difi'erent periods. 
First Period. — After the upheaving of the strata, already referred 
to, the beds, of course, were set on their edges (as in preceding 
figure), and were much fractured. The faults, too, which are so 
abundantly met with in the coal-measures, were no doubt produced 
by this upheaval. Consequently, in this state, the strata were 
