124 Horner*s Geological Address. 



ciirrence in the lower regions, particularly on the Siberian 

 side. The igneous rocks that enter into their composition 

 are different forms of syenite, porphyry, greenstone, and fel- 

 spar rocks, often graduating into each other, and associated 

 with serpentine. These have evidently been erupted at dif- 

 ferent periods ; and there are wide tracts occupied by grani- 

 toid rocks, which appear to have been erupted after the age 

 of the carboniferous series, and posterior to the greater pro- 

 portion of the greenstones and other eruptive rocks of the 

 Urals. 



It was only after Sir R. Murchison and his companions 

 had become thoroughly acquainted with the slightly con- 

 solidated and unbroken sedimentary deposits in European 

 Russia, that they were able to decipher the intricate charac- 

 ters of the indurated and crystalline strata which constitute 

 the flanks, enter into the very body, and form lofty serrated 

 ridges of the Ural chain ; broken up and cast about in much 

 apparent confusion. But from the presence of organic re- 

 mains, traceable at intervals along both flanks, and even close 

 to the axis of the chain, they w^ere satisfied that some of the 

 central ridges, although composed of chloritic, talcose, mica- 

 ceous, and quartzose slates, cannot be of higher antiquity 

 than the unconsolidated Lower Silurian rocks on the shores 

 of the Baltic ; and that others, although in a highly crystalline 

 state, are not older than the Devonian and Carboniferous 

 series. The same rocks, when they recede from the great 

 lines of eruption, resume their ordinary "Sedimentary charac 

 ters. In one place the authors expressly say, that, in pro- 

 portion as they receded from the igneous zone, the sediment- 

 ary strata gradually parted with their talcose, chloritic, and 

 quartzite characters, and assumed the appearance of ordinary 

 argillaceous schist, with bands of grit and sandstone, all 

 parallel to the crystalline axis of the chain. In another place 

 they describe certain Upper Silurian beds, consisting of al- 

 ternations of argillaceous slate and black encrinite limestone, 

 passing into talc-schist, and containing great flakes of mica. 

 Between two great parallel lines of eruption, they saw pure 

 white saccharoid limestone containing Encrinites, and asso- 

 ciated with other crystalline beds, which they were satisfied 



