366 Mr. George Tate on the Cheviots. 



shales, and thin cherty limestones are exposed. At the 

 point of junction at Linn brig they are highly inclined, 

 disturbed, and shattered, and some portions are torn from 

 the mass; they dip away from the porphyry at an angle of 

 75 degrees, which, however, lessens as the distance from the 

 porphyry is increased. 



To this formation I am disposed to refer a small isolated 

 patch of sandstone, filling up part of a deep narrow dene in 

 the porphyry, near to Cherrytrees, about one mile northward 

 of Yetholm. It is of limited area, but upwards of 50 feet in 

 thickness, in thin beds nearly horizontal, mostly soft, of 

 a dull red colour, and micaceous ; but other beds are less 

 micaceous and mottled with red, somewhat gritty, being 

 formed partly of small fragments of porphyry. Organic 

 remains I could not find ; but I have been told that casts of 

 small branches of trees have been seen in it. Porphyry sur- 

 rounds this sandstone, and there is no similar deposit within 

 two miles. Very probably the lower porphyry hills of this 

 district, towards the west and the north, had been covered by 

 sandstones of the Tuedian age, which have been removed by 

 denudation ; leaving this little patch, protected by the narrow 

 valley, to tell us some little of the history of the past. 



Origin. 



Some modern geologists are disposed to regard such plutonic 

 rocks, as granites and their allies, as metamorphosed sedimen- 

 tary rocks. M. Delesse, who has written with great ability 

 on metamorphism, distinguishes two kinds : first, normal or 

 general metamorphism, depending on causes which have 

 acted on a grand scale, but generally in an imperceptible 

 manner ; and secondly, abnormal or special metamorphism, 

 which depends on partial causes visible in their modes of 

 action and generally limited in extent. Of the abnormal 

 metamorphism there are many examples in the Border land, 

 affording clear evidence of the igneous origin of basaltic 

 rocks, and of their having, like lava, been in a heated and 

 molten state ; for the stratified rocks in contact with these 

 basalts are in several places, as at Ratcheugh, Holy Island, 

 Bamburgh, Dunstanburgh, &c., metamorphosed; limestones 

 have been converted into crystalline marble, shale into ribboned 

 porcellanite, coal into anthracite, and sandstone has been in- 

 durated. Such effects, however, nowhere appear on strati- 

 fied rocks adjacent to the Cheviot porphyry and syenite; 

 these strata are elevated, and in some cases contorted, but 



