GEOLOGY. 341 



only near the base of the sandstone series are compared with the west- 

 ern laccolites. 



It is satisfactory to find that the monoclinal structure of these Meso- 

 zoic areas is due to an arrangement not unlike that which is to be met 

 with in the Paleozoic and still older rocks along the western border of 

 the Atlantic belt from Quebec to Alabama, where, as the result of faults 

 with uplifts on the eastward side, the newer rocks not only seem to 

 pass beneath the older, but in many cases are actually overlaid by them. 

 J. J. Stevenson has lately re-examined and carefully mapped the suc- 

 cessive parallel faults in southwest Virginia, by which the basal beds 

 of the Paleozoic are repeatedly brought up against the coal measures. 



SEKPENTINE EOCKS. 



Serpentine was, by the older geologists, tegarded as intrusive, and 

 by many supposed to be derived from various eruptive rocks by a proc- 

 ess of metasomatosis, while others have supposed it to be formed, as 

 is doubtless often the case, by epigenesis from olivine rock, which was 

 iilso regarded as eruptive. The late studies by Brogger and others of 

 the olivine rocks of Norway have shown these to be clearly of aqueous 

 ■origin, and contemporaneous with the inclosing strata, thus supporting 

 the views of those who have always held to the aqueous origin of the 

 great rock-masses of serpentine. 



The serpentines of Anglesea, of Cornwall and of parts of Scotland are, 

 according to Bonney, to be regarded as intruded among the accompany- 

 ing crystalline schists, while Hicks and others regard these same ser- 

 pentines in Anglesea and in Scotland as contemporaneous stratified de- 

 posits in Huronian (Pebidian) rocks. The indigenous character of the 

 serpentines and gabbros from the granulite rocks of Saxony is, accord- 

 ing to Credner, not doubtful. These latter, as already noticed, are 

 probably to be referred to the Montalban or younger gneiss series, in 

 which, as Hunt has shown, are included also the bedded serpentines 

 and olivine rocks found in the Blue Eidge in North Carolina. 



The question of the eruptive or the indigenous character of the simi- 

 lar serpentine rocks (often containing olivine) found in the upper gneisses 

 of the St. Gothard has been discussed at length by Stapft, who has had 

 a favorable opportuity of studying them in directing the construction 

 of the railway-tunnel just opened through that mountain. He main- 

 tains, with regard to the origin of serpentines, the view first put forth 

 by Hunt, that the material of these serpentine rocks was originally de- 

 posited from water, as hydrous magnesian silicates, in conformably inter- 

 posed beds among the inclosing sediments. 



In the subsequent crystallization of the sediments he supposes the 

 magnesian silicate to have become an anhydrous olivine or enstatite- 

 rock, from which by epigenesis at a later j)eriod serpentine has been 

 formed, a process not yet complete, as shown by the presence of included 

 grains of olivine. Movements of the earth's crust by folding and fault- 



