140 OVERLYIN-G AND TRAP ROCKS. 



contain carbonaceous matter, this ingredient may also 

 assist in conferring fertility on the resulting soil. 



To enumerate the geographical situations of the 

 rocks of this division, would be an endless task, as 

 they occur in all parts of the world. In our own 

 islands, the western parts of Ireland, with the corre- 

 sponding eastern ones of Scotland, offer one conspi- 

 cuous, though scattered position for the recent traps, 

 extending quite across the latter country. And if 

 under much waste, and consequent separation, this 

 trap, or these traps, bear a singular coincidence with 

 the secondary strata, avoiding the primary, I am not 

 so satisfied with any explanation that I might now 

 suggest, as to trouble the reader with it. Of the older 

 porphyries, Glenco and its vicinity, with a district 

 near Inverary, offer the most extensive examples ; since 

 I feel very much at a loss respecting the age of those 

 so abundant in the south of Scotland and in Northum- 

 berland. On the continent of Europe, I may enume- 

 rate the traps of the Rhine, and the porphyries of 

 Sweden, of the south of France, of Saxony, Bohemia, 

 and Hungary, and those of Italy in the north. They 

 occur also between the Nile and the Red Sea, possess- 

 ing historical celebrity, and in the Ural and Altai 

 mountains. In the Andes, they are extremely conspi- 

 cuous, from their continuous superiority of position ; 

 but a work which I have laboured to the utmost con- 

 densation, perhaps not very judiciously, cannot find 

 room for details so extensive as the geography of rocks 

 demands. Some varieties of this family, in different 

 countries, contain metalliferous veins ; but they have 

 occurred chiefly in the older porphyries, including 

 copper, tin, lead, and silver, principally, with, occa- 

 sionally, manganese and gold. 



