GEOLOGY. 



By Prof. T. Steery Hunt, LL. D., F. E. S. 



EOZOIC EOCKS. 



The study of tlie Eozoic, or, as they are often called, the Archaean 

 rocks — the Primary rocks of older writers — continues to occupy more and 

 more the attention of geologists. It is now generally understood that 

 these rocks, like those of Secondary and more recent periods, are capa- 

 ble of subdivision into great stratitied groups, the relations between 

 which, in the absence of organic remains, must be determined by strat- 

 igraphical and lithological characters. Of these, three great groups — 

 first established in North America, and named Laurentian, Huronian, 

 and Montalban — are now recognized in many parts of the old World. 



The existence in the Alps of an older granitic gneiss, corresponding 

 to the Laurentian, and a younger gneissic series, the representative of 

 the Montalban, has long since been recognized by Gerlach, Gumbel, 

 and others, and the relations of the former to the great greenstone or 

 pietre verdi series of northern Italy, rightly referred by Gastaldi to the 

 Huronian, has attracted attention. It should, however, be said here 

 that this series, as defined by him, included also the younger gneisses 

 Geological studies of the Simplon, with reference to the proposed rail- 

 way-tunnel through the mountain, made by Eenevier, show the exist- 

 ence there of an older gneiss, called by Gerlach the gneiss of Antigorio, 

 which is well seen in the Val de Vedro, where it is brought up by an 

 anticlinal from beneath a mass of younger gneisses, with micaceous and 

 hornblendic schists and crystalline limestones. This latter series has 

 a great thickness, and is probably, like the upper gneiss of the St. 

 Gothard, JMontalban, here resting directly upon Laurentian. 



The careful geological studies of Stapff, the director of the St. Goth- 

 ard tunnel, show at thebase a granitoid gneiss (veined granite of other 

 observers), to which belongs the Finsteraarhorn, overlaid by a great 

 series of gneisses and mica-schists, with serpentine and hornblendic 

 rocks, through which the greater part of the tunnel passes. These form 

 the southern slope of the St. Gothard, as well as the basins of Unsereu 

 on the north and the Ticino on the south side. They have, according 

 to Stapff, an aggregate thickness of not less than 15,000 meters, 

 but the possibility of repetition by faults and undulations should not 

 be lost sight of. Von Hauer has recognized two similar series of 



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