470 MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 



cause may be supposed to have occasioned, seem to accord well enough with the 

 actual phenomena. 



If, then, the convulsive movements which the greywacke system has under- 

 gone, he attributable to changes in the earth's nucleus, these changes must have 

 occurred in certain lines, so as to have produced the remarkable uniformity 

 of direction and parallelism which prevails among the ranges and strata of grey- 

 wacke. But this is a question which lies still beyond the depths of modern phi- 

 losophy. 



2. The next important change in this part of the island seems to have been 

 the eruption of the felspathic rocks which form the Cheviots, the Eildons, and 

 those other hills, shewn in the first part of this Memoir as belonging to the same 

 epoch with them. 



It is quite manifest that these felspathic rocks, generally speaking, were 

 erupted long before the great mass of the greenstones and basalts appeared. The 

 same remark holds true in most other districts, as there cannot be a doubt that 

 the felspar rocks of St Abb's Head, Soutra Hill, the Pentlands, the Ochils, and of 

 the hills near Comrie (Perthshire), burst out long before the augite rocks of these 

 several districts. 



Whether these felspathic rocks were erupted at the same time with, or imme- 

 diately after, the elevation of the greywacke strata, is uncertain. At all events, 

 they were not erupted previously, for in many places these felspathic rocks are 

 seen intersecting the greywacke strata, and in some instances containing por- 

 tions of greywacke rock. Moreover, those places where the strike of the grey- 

 wacke strata deviates from its east and west bearing, are mostly to be found near 

 the Cheviot and Eildon porphyries. At the same time, the outburst of these 

 igneous rocks seems, to a very considerable extent, to have been controlled by 

 pre-existing vertical strata of greywacke. Thus, most of the felspathic dykes run 

 east and west. Even the larger outbursts, as the Eildon Hills, exhibit, generally 

 speaking, an elongated shape, of which the greater axis runs in the same direc- 

 tion. 



It would appear that felspathic rocks, after then* first great outburst, con- 

 tinued to be erupted, though in a gradually diminishing degree ; for we have 

 seen, that a number of felspathic dykes intersect the conglomerate of the old red 

 sandstone. 



3. The next circum stance deserving of attention is, that all the geological 

 convulsions just described, happened when this district was under the waters of 

 an extensive ocean. 



(1.) The depressions of the greywacke formation produced by the causes 

 above alluded to, as well as the hollows among the outbursts of felspathic rock, 

 were gradually filled up with the debris of these several rocks exposed to the 

 action of submarine currents. In this way beds of conglomerate, consisting of 



