memoir of the Geological Survey. In other instances, although the individual blocks are not large, there are evidently local accumulations of fragments from the same bed, perhaps the deposits of single icebergs. The most notable example of the former kind is that of Linksfield, which has been several times brought under the notice of this Society ; while striking instances of the latter kind occur at Inverugie, Lhanbryd, and Urquhart; these and similar cases have led to reports of the existence of Secondary strata in situ, afterwards proved to be erroneous*.
With regard to the general relations of the patches of Secondary strata in the east of Scotland to the great masses of Palaeozoic age which constitute the Highlands, the conclusions to which Sir Roderick Murchison appears to have been led by his first examination of the strata on the east coast of Sutherland were as follows : — That the Jurassic beds were deposited in a basin formed of the Old Red Sandstone- rocks, and that subsequently a great upheaval of granite in a solid condition caused the vast amount of disturbance and contortion seen in some parts of the strata of the former series†. Later observations appear to have convinced Sir Roderick Murchison that some portions of what he originally regarded as a granitic rock, were really stratified and metamorphic‡; but he has not in his later writings sought to harmonize this fact with the theory of the relations of the rocks which he originally put forward. In the section across Sutherland, published in the 'First Sketch of a Geological Map of Scotland' in 1861 §, the Old Red Sandstone and the Jurassic series are represented, probably through inadvertence, as following the Silurian in nearly conformable sequence.
Mr. Hay Cunningham, in his examination of the county of Sutherland in 1839, clearly perceived that all the southern part of the crystalline rocks, against which the Jurassic strata of that country lie, are really stratified and metamorphic, and not granitic. In his map he indicates, with tolerable correctness, the range of these metamorphic rocks, though he does not carry them sufficiently far to the southward || ; and he further identifies them with the great series of gneissic rocks which covers so large a part of Sutherland. Rejecting, on these grounds, Murchison's explanation of the peculiar phenomena of the district by the upheaval of granite in a solid condition, Mr. Cunningham himself put forward a theory to account for them, which, however, is likely to find but little acceptance among geologists at the present day. He argues that the Jurassic strata might have been originally deposited in their present condition of high inclination, and that the "brecciated" appearance
- See Duff, ' Geology of Moray,' 1842 ; Prestwich, Quart. Journ. Geol. Soc.
vol. ii. p. 545 ; Hugh Miller, 'Rambles of a Geologist,' &c. 1858 ; &c. &c.
† Trans. Geol. Soc. 2nd ser. vol. ii. pt. 2. pp. 295, 307, 354, &c., pl. 31.
‡ Ibid. pt. 3. p. 355.
§ This Map is republished in Geikie's ' Scenery of Scotland,' 1865.
|| See also the Map published by the Rev. J. M. Joass, to illustrate the distribution of the auriferous deposits in Sutherland, Quart. Journ. Geol. Soc. vol. xxv. (1869), pl. xiii.
