42 MR STEVENSON ON THE GEOLOGY OF COCKBURNLAW, 



among these hills. At several localities, series of specimens may be obtained, 

 shewing the gradual transition from the unaltered greywacke, to where it becomes 

 converted into syenite, which again passes into granite ; and the latter, in its 

 turn, graduates into porphyry, — the progress of transformation being so gradual, 

 as to render it very difficult to decide where the characters of the aqueous rock 

 become merged in those of the u/neous. In many cases, the only way of distin- 

 guishing the original planes of stratification fi'om those of cleavage, which have 

 been superadded in the metamorphic process (unless, indeed, we can trace the 

 strata uninterruptedly from where they are unaffected), is by the schists which 

 alternate with the greywacke. These are sometimes much contorted, and present 

 the appearance of hornblende slates. 



While the greywacke is thus altered, wherever it approaches the granite or 

 porphyries, the old red sandstone strata, being of a date subsequent to that of the 

 eruption of these older traps, are unchanged even at the place of contact. This 

 is seen on the SW. side of the Staneshiel, where the red sandstones are tilted up 

 against the granite at high angles, without any appearance of alteration,— the 

 granite and overlying sandstones having, in this instance, been elevated (as we 

 shall hereafter shew) by the agency of the augitic traps. 



Porphynj of the Knock Hill. — This rock is of a grey colour, having a felspathic 

 basis, and containing a considerable quantity of carbonate of lime. The hill to 

 westward of Bmiihouses consists of the same rock, and is connected with the 

 Knock hill by a ridge running in a SSE. direction. To westward of the felspathic 

 mass of the Knock hUl, the greywacke appears in nearly vertical strata, with a 

 NNW. strike, and is considerably altered by the proximity of the igneous rock, 

 being hard and full of quartz veins. On the east side of the hill, and within a 

 few feet of the porphyry, the red sandstones are seen tUted up at high angles, and 

 even partially retroflexed ; but being of more modern date (as in the case of the 

 junction of the granite and sandstones on the west side of the Staneshiel), they 

 shew no traces of metamorphism, but remain quite fresh and soft ; and the re- 

 mains of scales, &,c., of the Dendrodus which they contain still preserve their 

 original colour. Similar appearances are also observed in the vicinity of the por- 

 phyry in Kidshielhaugh. 



2. Augitic Traps. 

 Rocks of this class also abound in the form of dykes, beds, and irregular 

 masses, and consist of several varieties of greenstone, basalt, amygdaloid, and trap 

 tuff. These have all been erupted subsequent to the deposition of the old red 

 sandstone and lower coal measures, as is evident from the disturbance and meta- 

 moqjliism apparent in these strata, whenever they approach to traps of this class. 

 With one or two exceptions (to be hereafter noticed) they do not appear in con- 

 tact with the older rocks, being confined to the secondary strata, which are much 



