628 FOURTH REPOUT — 1S34. 



to the most violent disturbance and dislocation. Through a g^reat 

 many different parts of the red sandstone girdle, flanking the 

 hills, the trap is now seen protruding, and bearing, far above the 

 rest of the surface of the surrounding country, the red sandstone 

 strata on its top or sides. 



At Home Castle, which is built upon basalt, a large quantity 

 of the sandstone is seen enveloped in the trap. The whole mass 

 of trap here is very considerable, and may be perhaps altogether 

 two miles in circumference. Home Castle is about 200 or 250 

 feet above the red sandstone plains surrounding it; and very 

 near its walls the red sandstone above referred to may be seen 

 verj^ highly inclined, leaning upon the basalt. There are various 

 other hills of trap, which occur among the old red sandstone 

 strata, such as the Dirringtons, Lamberton Hill, Kyles Hill, 

 Eildon Hill, &c. The protrusion of these immense masses of 

 trap (some of them forming hills 1000 or 1200 feet above the 

 level of the sea, and 300 or 400 feet above the surrounding coun- 

 try,) could not have failed to elevate the district immediately in 

 contact with them, and the effect of this elevation must neces- 

 sarily have been to produce great rents or fissures across the 

 strata so elevated and disturbed. Suppose that by the eleva- 

 tion of Home Castle rock, for example, the red sandstones, 

 which were originally horizontal, wei-e pushed upwards so as to 

 raise one part several hundred feet above the surrounding coun- 

 try ; the width of the cracks or rents caused by this elevation, 

 and their extent through the country, would, of course, depend 

 upon the height to which the strata were raised, and the di- 

 stance to which the disturbing force operated. But one thing is 

 evident, that these rents or fissures would genei-ally run from 

 the point of highest elevation or greatest disturbance as a centre ; 

 and whilst there the rents would be of considerable width, they 

 would gradually diminish in width in proportion to their di- 

 stance from that centre. This observation is well illustrated by 

 what actually occurs in the neighbourhood of Home Castle ; for 

 two or three trap-dykes (to be afterwards more particularly de- 

 scribed) are found to run across the country for several miles from 

 that point as a nucleus, this nucleus having served as the source 

 or fountain-head to supply the different currents of trap which 

 now form the dykes that have filled up these extensive rents. 



These trap-rocks seem to be generally confined to the old red 

 Bandstone group, and occur more frequently next the edge of 

 the group contiguous to the hills than to the one more distant 

 from them. 



There are several instances of the lower conglomerate having 

 been cut through and hardened by veins of trap ; indeed, in one 



