I i le ae eee 
Geology of Cockburn- Law. 367 
By William Stevenson, Dunse. Communicated by David 
Milne, Esq. 
The author, in the first part of his paper, described the nature of 
the formations, and in the last part offered his views in explanation 
of the appearances. 
In describing the formations, he enumerated, first, those of aqueous, 
and last those of igneous origin. 
I. The former consist of the greywacke, the old red sandstone, 
and the coal formation. 
(1.) The greywacke strata form the summit of Cockburn-Law, 
having a strike about NE. and SW. nearly vertical. There appears 
to be no decided evidence of any organic remains in these strata ;— 
there are curious markings which are most probably only concretion- 
ary. At Hoardwheel, situated to the eastward of Cockburn-Law, 
two varieties of copper ore are found in the greywacke, the green 
and the grey, the former of which is the most plentiful, and imparts 
a beautiful hue to some of the rocks. The oxide of manganese is also 
widely diffused. 
(2.) The old red sandstone strata lie over the vertical strata of 
the greywacke. At a distance from the hills they are generally ho- 
rizontal, or dip away at a gentle angle ;—but at the sides of the hills 
they are highly inclined. These old red sandstones are extensively 
developed in Preston Haugh. The lowest bed consists of both angu- 
lar and roundish greywacke and porphyritic portions. The colour of 
this formation is, especially towards its base, of a red colour. 
It is in this formation, that the bones, teeth, scales, and spines of 
the Holoptichius nobilissimus, a large ganoid fish, are found. These 
interesting relics are very abundant in the strata opposite to Cock- 
burn Mill, and also about half a mile below it, on the right bank of 
the Whitadder. 
(3.) The strata of the coal-formation lie above the old red sandstone 
rocks in a conformable position. They are to be seen in the Whit- 
adder, below Preston Bridge, and consist of the ordinary sandstones, 
shales, and strata of ironstone. The only fossils prevailing in them 
are those of terrestrial vegetables. 
II. The Igneous rocks were divided by the author into two classes 
—one of which he described as the Felspathic, the other as the 
Augitic. 
(1.) The Felspathic rocks comprehend all those igneous rocks 
associated with the greywacke strata, consisting of the granites, 
and syenites, and old porphyries of Cockburn-Law, the Staneshiel, 
the Knock Hill, Blackerstone Hill, &c. 
(2.) The Augitic trap-rocks exist almost entirely among the more 
recent aqueous rocks, viz., the old red sandstones and coal-measures. 
They are seldom or never seen within the range of the greywacke 
formation, at least in this neighbourhood. 
