14 GEOLOGY OF THE LOTHIANS. 



conglomerate ; and, when very compact, its mechanical na- 

 ture is not very easily recognised. The Clay-slate, which is 

 frequently associated with the greywacke, into which it 

 passes, and with which it alternates, is of various shades of 

 ash, bluish and smoke grey. Its general aspect is eart hy, 

 and it never assumes that crystalline appearance which emi- 

 nently characterizes that of an older formation, viz. the slate 

 associated with gneiss and mica-slate. In the strata of grey- 

 wacke there is also sometimes a striped appearance, identi- 

 cal with that exhibited by the coal formation shales, and, in 

 some districts, it contains numerous minute veins of mas- 

 sive quartz, and layers of red haematite. The uniform 

 sameness of the mineral characters of the Transition 

 rocks, in countries far removed from each other, is a proof 

 that the causes, from the actions of which they resulted, 

 were almost universal ; a fact which is at complete vari- 

 ance with that system of geology, which sees only in the 

 various rocks of our continents the long-continued action of 

 existing causes. By the term " universal," however, it is 

 not intended to be implied that at one period the earth 

 was covered completely by an envelope of greywacke strata. 

 Such an opinion, either in regard to it or any other forma- 

 tion, is contradicted by every appearance. But it is wished 

 to be only understood as intimating that, during the epoch of 

 the greywacke's formation, it is probable that, when deposi- 

 tions of strata took place over the globe, they were in cir- 

 cumstances which allowed only the deposition of a grey- 

 wacke. The idea which supposes, that, if a deposition of 

 strata took place, that deposition must in all parts be simi- 

 lar, because there existed a series of causes over the whole 

 globe, which if called into action produced the same effects, 

 is quite different from that which assumes that these causes 

 acted at one given period over the whole globe. If all 



