20 MONOGRAPH OP DURA DEN. 



influence of the causes which produced their elevation. The 

 quartz of the granite constitutes the substance of some of the 

 more precious gems ; the mica is divisible into plates of the 

 three hundred-thousandth part of an inch in thickness, and 

 enters as an ingredient into almost every combination of rock ; 

 the felspar is reduced to clay, and, mixed with the hornblende, 

 forms the soil of our most fertile carses. Here also among the 

 primary series — wherever existing on the globe — is the vein of 

 the silver and the gold and all the rare metals, and the 

 emerald, sapphire, beryl, topaz, and amethyst all nestle in their 

 crystal cavities. The marble to decorate our temples, the 

 slates to furnish a commodious roofing to our dwellings, the 

 granite to give endurance to our monuments, are among the 

 first of Nature's offerings ; and thus combining security and 

 elegance, usefulness and beauty, richness and variety, the foun- 

 dations of our steadfast earth, and arrangement of its mineral 

 wealth, are well calculated to speak the praises of its muni- 

 ficent Creator, and to form a noble subject of contemplation to 

 its intelligent inhabitants. 



The primary series of rocks now described are followed, as 

 represented on the Section, by a coarse conglomerate of 

 great depth and extent (b). Grey and red fine-grained sand- 

 stones rest unconformably upon this mass, intermixed every 

 where with outbursts of trap or the igneous rocks [f e d c x). 



The large boulder conglomerates of Caithness, Sutherland, 

 and Orkney, first described in the conjoint papers of Murchison 

 and Sedgwick, and recently so admirably worked out in all 

 their bearings in the appendix of the new edition of Siluria, 

 may be considered as the true equivalents, in age and position, 

 of the great conglomerate masses that flank the southern out- 

 liers of the Grampians. These rocks contain large portions of 

 all the primary series, rolled as well as angular, some of which 

 arc eight or ten feet in diameter. They are deej)ly cut, and 

 beautifully exposed to ^iew, by the wearing channels of the 



