86 GEOLOGY OF THE LOTHIANS. 



jasper, chalcedony, and cachalong : they run a determined 

 course ; and in breadth vary from the smallest size to two 

 feet. The fact of there being exhibited in the structure of 

 the larger of these veins evident marks of mechanical actions, 

 renders it probable that none are of an origin contempora- 

 neous with the trap. Many of the veins are composed of 

 an aggregate of fragments of white and black hornstone, 

 cemented together by a similar basis ; all these fragments 

 are angular, and frequently they may be reunited to each 

 other in the imagination. A.s to the variety of the horn- 

 stone which constitutes these fragmentary masses, or forms 

 the base which contains them, there is no regularity ob- 

 served, for in some portions of a vein the masses are of 

 black hornstone, imbedded in a white hornstone ground, 

 while, in other parts angular fragments of white hornstone 

 are inclosed in a base of the black. To explain the mode 

 in which these veins have been formed in the existing state 

 of knowledge in regard to this subject is perhaps impossi- 

 ble ; an infiltration from above, however, of the minerals 

 which constitute them, is the most probable mode of their 

 formation, while a breaking up of the previously formed 

 veins and their reconsolidation, by a new infiltration of 

 quartzose matters, may have effected those appearances 

 which indicate mechanical actions. 



Concerning the relations of the porphyry of the Pent- 

 lands to the strata which skirt their southern base, little 

 can be said, inasmuch as there are no natural or artifi- 

 cial openings sufficiently near the junction of the two rocks. 

 In the bed of North Esk river there is almost throughout 

 its whole course, a fine section of the various strata of the 

 coal formation, but in no part are they in any way connected 

 with rocks of ignigenous origin, though that they have 



