1848.| NICOL ON THE SILURIAN ROCKS OF THE TWEED. 203 
extremity on the German Ocean, described by Dr. Hutton and Sir 
James Hall, the beds are seen to be as it were crushed and folded 
together. I have observed similar appearances, though on a far less 
magnificent scale, in many places in the interior. We may therefore 
conclude that this structure is common to the whole chain, which 
will thus represent an immense fold or wrinkle in the rocky crust of 
the globe. This fold cannot be ascribed to any of the igneous rocks 
now in contact with the strata. The interstratified felspar porphyries 
are quite inadequate to this effect, even where most abundant ; and 
in many parts of the formation are very rare. The porphyries of the 
Cheviots and Pentlands are still less capable of having effected this 
immense change, as they are more recent than the sandstones which 
rest on the elevated greywacke, and thus cannot be the cause of this 
elevation. The same facts in like manner exclude the augitic trap 
rocks, whether on the north or south. These conclusions are chiefly 
negative, but the followimg may perhaps lead to some positive con- 
clusion on the question. In the greywacke, we have seen, no frag- 
ments of the primary strata i the north of Scotland occur. In the 
red sandstone in the central district of Scotland such fragments are 
common, and hence, in the interval between the formation of the 
greywacke and that of the red sandstone, these northern rocks must 
have been raised up and subjected to abrading influences. I have 
thus been inclined to believe, that that invasion of igneous agencies, 
which hardened and metamorphosed the gneiss and mica-slate in the 
Scottish Highlands, at the same time crushed up and folded together 
the transition beds of the southern or border counties. The pre- 
valence of high angles and an irregular dip on the northern margin 
of the formation gives some confirmation to this theory. We may 
then believe, that whilst the gneiss and mica-slate of the Grampians 
were crystallizing in the interior of the globe, the more sedimentary- 
lookmg formations of the Lammermuirs were rising up into lofty 
mountains, which have since been worn down under the action of 
various external agents. 
I have hitherto avoided any allusion to the organic remains occur- 
ring in this formation, bemg desirous that the conclusions deducible 
from the physical structure and conditions of the mass should stand 
on their own foundation. It is only very recently too that any organic 
remains have been found in this district, or indeed in the whole 
transition formation in the south of Scotland. The first notice of 
them is by Dr. Hutton in his ‘ Theory of the Earth,’ who states that 
he found shells m a limestone quarry at Wrae, near Broughton, on 
the road from Edmburgh to Dumfries, but, as was to be expected at 
that time, gives no further account of them. The quarry is in a 
remote and little-frequented part of the country, and seems to have 
been rarely resorted to by scientific collectors. Some years ago I visited 
it, but found it wholly forsaken, and the limestone rock so concealed 
by debris that its very existence seemed problematical. Last autumn 
I again visited the place, and succeeded im finding some fragments of 
limestone among the slate debris from which I obtained a few im- 
perfect fossils. The rocks in this place are the usual slates and 
greywacke, with numerous veins of quartz. The slate has been 
