44 GEOLOGY OF THE LOTHIANS. 



origin was Neptunio- Plutonic. If we suppose the existence 

 of a sea sufficiently deep to allow of the eruption of igneous 

 matter, without their assuming a vesicular structure, and 

 that, by the decomposition of older trap rocks, there was 

 produced a series of more or less regular strata, accidents 

 may be found fitted for the formation of the trap-tufas and 

 their alternations with basaltic and greenstone masses. As 

 the comparatively modern tufas of -flitna are traversed by 

 veins of basaltic lava, so the more ancient tufa of the car- 

 boniferous epoch is traversed by greenstone and basalt, — 

 the posterior formation of which is evinced by their pro- 

 ducing changes, more or less similar to those which they 

 effect upon rocks of aqueous formation. 



The structure of the trap-rocks is never vesicular, and 

 all their relations to associated masses are such as indicate 

 that their formation and the changes which they have 

 produced, were effected under a compression sufficient for 

 a perfect crystallization of the rocks from a fluid state. 

 Through all the districts in which they occur, there is, 

 in the arrangements of the trap-rocks, nothing partaking 

 of that aspect which characterizes the volcanic cone — 

 no hills formed of consolidated igneous matters arranged 

 concentrically. There are, however, many analogous ap- 

 pearances ; for the marks of fracture, upraisure, and all the 

 indications of altered states of the Neptunian formations, be- 

 come gradually less apparent as the strata recede from the 

 masses which are to be considered as the disturbing agents. 

 In regard to the question, Whether have the unstratified 

 rocks of the Lothians been the product of one eruption, or 

 have they been sent from below at different periods ? no 

 very satisfactory answer can be given, the want of sections 

 exposing their mode of connection, rendering this impracti- 

 cable. From the circumstance of finding, however, in a few 



