On the Geology of Kelso, 145 



the increased liardness of the stone, and the collection of 

 the white substance into sub-globular concretions. Where 

 the change has proceeded further, this substance has as- 

 sumed, more or less perfectly, the crystalline form of fel. 

 spar. As the altered rock only occasionally appears above 

 the surface, in this place, the observer has but few oppor- 

 tunities of examining it : one of these, however, deserves notice. 

 About a mile from Yethoim, east of the road, near a stream, a 

 small portion of the rock is visible, on examining which, the 

 altered sandstone is found in contact with a greenish felspar, 

 containing crystals and concretions of the same substance* 

 Whether this is the sandstone, still more altered, I shall not 

 venture to say ; but this is not improbable, although it is found 

 high on the Cheviots. Well aware of the various sources of 

 error which prevent inquiries of this nature from being satis- 

 factory, I valued but little, at the time, the observations made 

 near Yethoim. Although my experience as a geologist — if one 

 may assume that much abused title, who carries a hammer only 

 for amusement — is but limited, it may be interesting to notice 

 some of the sources of error to which I have referred, as it will 

 enable me to introduce a few observations, made in a country 

 abounding in remarkable geological phenomena. When a 

 pyrogenous rock, in forcing its way to the surface, breaks 

 through, and is much mixed with, a sedimentary deposit, they 

 occasionally form a breccia, in which the characters of both rocks 

 are in some degree altered. The former, acting as a cement, is 

 frequently earthy or granular, while the fragments of the latter 

 exhibit proofs of having been heated, and — which deserves 

 notice — are often penetrated by the cement, to a degree that 

 renders it difficult to distinguish them. The characters of the 

 mixed mass, thus formed, will vary, according to the degree of 

 friction to which it has been exposed, and to the distance from 

 the pyrogenous rock. The latter is often mixed to a consider- 

 able depth, with matter derived from the mass through which it 

 has broken, so finely divided as to alter its characters but little; 

 and where no part of it in a purer state is visible, the whole 

 may easily be mistaken for an ordinary mechanical deposit, 

 altered by heat. A case somewhat similar to this occurs at 

 Pwllheli, in Carnarvonshire, where compact felspar is intimately 



VOL. XXVI. NO. LT. JANUARY 18 J9. I 



