1897.] NATURAL SCIENCES OF PHILADELPHIA. 415 



chew is distinguished by a great variety of forms; i. e., numerous 

 remains of ostracodes, cephalopoda, Platyceras, representatives of 

 Hercynella (H. bohemica), and peculiar conchifers ( Vlasta Dalila)." 



In the section this limestone apparently rests conformably on the 

 group "M" of metamorphic schists and quartzites, which is thus 

 assumed to be of lower Devonic origin. 



The lower division of the Devonic is thus described (1. c, 10) : 



" It has great petrographic diversity. The varieties most devel- 

 oped include quartzose sandstone without feldspar, arkoses and 

 conglomerates. These are the rocks that form the ridges of the most 

 considerable parallel chains of the South Oural. In the eastern 

 summits is observed a gradual transition from sandstone, arkoses 

 and conglomerates, to compact quartzites, charged more or less with 

 mica. The lower schist is a black sericitic schist, giving a steel gray 

 sometimes silky reflexion on the surface. Frequently the passage 

 of these schists to micaceous and chloritic varieties, very rich in 

 magnetite and iron oxide, can be observed. Taking up quartz these 

 schists pass into micaceous and talcose quartzites. In places the 

 black argillaceous schist shows inclusions of large crystals of pyrite 

 and pseudomorphs of pyrite in limonite. This black schist is asso- 

 ciated in the lower part of the bed D\ g with a sericitic schist 

 nearly of the same composition as the black, but poorer in carbona- 

 ceous matter, and therefore of lighter color." 3 



" The rock most largely developed in the underlying group M 

 is a mica schist composed of quartz and mica, to which is ordinarily 

 joined a greater or less quantity of chlorite and magnetite. The 

 element of greatest interest in these mica schists, and chloritic mica 

 schists, is the orthose, which occurs in irregular and often broken 

 fragments. Very often these are enclosed in grains of quartz or 

 mica. Indications of the substitution of quartz and mica abound in 

 the cleavage of these orthoses. Tourmaline, and in the neighbor- 

 hood of Slatooust, garnets and staurotide are the most frequent in- 

 clusions in the mica schists." 



" Besides these schists the crystalline region comprises M a series of 

 argillo-schistose rocks which show the transition of typical phyllites 

 into the clastic argillaceous schists of the lower Devonic. The 

 massive rocks of M are represented only by granites and diabases. 

 Among the granites can be distinguished the gneisso-granites and the 

 coarsely crystalline porphyritic granites resembling what is called 

 Rappakiwi from Finland, which is much used for building, and forms 



3 See preceding page. 



