ALTERED ROCKS AND SPRINGS OF NIJNY SERGINSK. 
357 
they pass, however, into amorphous masses of quartz rock, in which nearly all 
traces of bedding are obliterated, whilst points of intrusive greenstone appear at 
intervals. 
He who disbelieves in the theory of metamorpliism may here be convinced of its 
truth. In the short space of a mile, since he can walk upon the edges of the partially 
altered beds of grit and schist, until he finds them converted into amorphous quartz 
rock, in contact with highly crystalline greenstone, a rock which, from its com- 
position and from the part it plays in all parts of the world, is now admitted to be 
of igneous and intrusive character. 
We came to the conclusion, that this sandstone and quartz rock are of the age of 
the millstone grit, because certain limestones which rise up behind them are clearly 
referable to the carboniferous limestone. In the environs of this Zavod we could 
not, it is true, discover any clearly definable organic remains, so very much had the 
rock been altered ; but the strata having a persistent strike from south-south-west 
to north-north-east, we observed that in following the same calcareous courses 
from Nijny Serginsk to the north, they became less altered, and regaining in a few 
miles the character they present upon the high road near Grobovo, contained many 
carboniferous fossils ( Bellerophon , Pecten, Cyathophyllum, &c.). By tracing these 
calcareous fossiliferous masses to the south-south-west or towards the points of 
eruptive matter, the changes are most marked. In the quarries where the lime- 
stone is extracted as a flux for the iron ores, it is first found to become highly fetid, 
veined and heavy, and next it is thrown over in arches and domes, the angles of 
inclination varying at every step. In this condition, though the rude outline 
of organic bodies is discernible, no distinct forms can be traced. Passing on to 
the south of Nijny Serginsk, the limestone, in a metamorphic amorphous state, 
rises abruptly into a low ridge which presents a rude escarpment to the river Sirga, 
from the base of which the mineral spring issues. 
A close analysis of mineral waters formed no part of our scheme, and we there- 
fore contented ourselves with tasting the spring, which is very copious, and much 
resembles that of Harrowgate in Yorkshire, being equally, we believe, saturated with 
sulphuretted hydrogen. The chief geological interest, however, consists in the 
fact, that whilst the limestone from which the spring issues is a highly crystalline 
amorphous mass, in which all traces of bedding and fossils have disappeared, and 
angular joints and rifts pass through it in all directions, hills of porphyry and 
