ALTERED ROCKS NEAR BOGOSLOFSK. 
397 
of Bogoslofsk as Silurian, but we now proceed to show, how after being intruded 
upon by igneous rocks, these strata are overlapped by courses which must, we 
think, be included in the Devonian system. (PI. II. fig. 6.) 
The rock which immediately overlies the red limestone in the southern suburb 
of Bogoslofsk seemed to us, at first sight, to belong to the group of trapppean 
rocks formed contemporaneously with the sedimentary deposits, for it occurs 
in regular beds of about one foot thick and dips 45° to the east. By close 
examination, however, M. Rose has shown that, though effervescing with acids, 
and having some resemblance to compact augite porphyry or greenstone, it 
exhibits, when disintegrated, a true brecciated or conglomerate nature. Pie also 
mentions courses of associated jasper in it, and as we agree with him and Colonel 
Helmersen, that this stratum of “quasi” igneous rock is surmounted by an 
agglomerate or breccia of angular fragments of fossiliferous limestone, and that 
these and the associated grauwacke schists (often jaspidified) are succeeded by a 
mass of augite porphyry, there can be no doubt, that eruptions took place after 
the consolidation of the sedimentary strata ; and that here, as in many other places, 
the igneous matter has for a certain space been injected in bands parallel to the 
laminse of the pre-existing deposits. Whatever this rock be termed, though clearly 
of plutonic origin, it is regularly bedded and jointed, and alternating with the 
grauwacke schists, dips with them decisively to the east. By this inclination the 
whole group above mentioned is brought under another course of limestone upon 
the east, in which a specimen of Brontes Jlabellifer was observed. From the pre- 
sence of this Eifel fossil and certain corals, we were therefore disposed to view the 
strata which overlie the Pentamerus limestone as Devonian. However difficult it 
may be to draw the line of separation between the Silurian and Devonian rocks, 
still this little section near Bogoslofsk seems to show, that whilst the great mass of 
the Silurian rocks may be metamorphosed towards the central axis of the chain, the 
uppermost beds at all events seem to pass into the Devonian strata in the environs 
of the Zavod 1 . If a section be made to the higher mountains of the Ural, which we 
T. camelina, V. Buch ; Spirifer vetulus, S. superbus, Eichw. ; S. rostratus, V. Buch ; Orthis Arimaspvs 
Eichw.; 0. elegantula (0. orbicularis, Sil. Syst.) ; Pentamerus Knightii, Sil. Syst. (since separated by us 
and named P. Vogulicus ) ; Pleurotomaria ( Turritella ) cingulata (His.), with the corals, Favosites Gothlandica, 
F. polymorpha , Astrtea porosa, Cyathophyllum cerulites, &c. From this assemblage M. von Buch consi- 
dered this limestone to be Upper Silurian, and probably of the age of the Ludlow and Aymestry rocks. 
' That Devonian rocks exist in the tracts north of Bogoslofsk and Petropavlosk, seems probable, 
judging from the fossils collected by Capt. Strajefski. 
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