140 GEOGNOSY AND GEOLOGY. 
at one time so much more intense at the surface than subsequently, 
produced great changes in the fine, loose, badly conducting matter 
deposited from the water. The stratification of bottom rock masses is very 
decided, and in many cases is effected by micaceous substances. -The 
strata generally stand at considerable angles to the horizon, sometimes 
nearly perpendicular, and not seldom entirely inverted: fan-shaped and 
arched strata in every variety also occur. The principal species of rock 
are gneiss, mica schist or flagstone, chlorite schist, and tale schist. These 
form the principal mass, and stand more or less in connexion ; while the 
subordinate masses to which steatite, dolomite, and marble belong, are 
confined to single beds and limited districts. The bottom rock is very rich 
in mineral substances, as various silicates, metallic oxydes, ores, metals, and 
metalloids. Of metallic oxydes magnetic iron ore is the most abundant; 
the ores are generally mixed with arsenic and sulphur; the native metals 
are gold, silver, and copper; the metalloids principally carbon in the form 
of graphite and sulphur; this latter of rare occurrence. This rock 
never contains fossil remains. The occurrence of abnormal masses in 
it is of especial importance; between these and the mass of the bottom 
rocks it is often difficult to draw a line of distinction. 
A definite order of succession is frequently exhibited among the members 
of the bottom series, which, however, is not constant. The gneiss is 
generally the lowest. It occurs in all modifications, in one place as 
common, in another as granitic; and again, but more rarely, as hornblende 
or tale gneiss. Its stratification is more or less evident, sometimes partially 
or entirely curved, sometimes straight. It sometimes exhibits a wood-like 
structure, depending on an extension of its components, in which case it 
splits, not into plates, as is most usual, but into pieces like billets of wood. 
Naumann, who has minutely investigated this feature in gneiss, calls it 
linear parallelism. The mica schist or flagstone, which generally overlies 
the gneiss, resembles it closely in its external character Next to this come 
chlorite schist and talc slate, either separately or together. Instead of the 
chlorite schist we frequently have chlorite rock, this generally exhibiting a 
coarse stratification. ‘These primary masses sometimes run one into the 
other, in such a manner as to render it difficult to draw the line of 
distinction; and although generally succeeding each other in the 
above-mentioned order, yet not unfrequently they alternate. 
Subordinate masses of the bottom series are the following: 
Hornblende flag and hornblende schist, which run into each other ; their 
place is next to the mica schist, with which they alternate. This is the 
“manner of their occurrence in the St. Gothard, and in several districts in 
Sweden. The place of the hornblende schist is sometimes assumed by 
hornblende rock. The stratification of these subordinate masses is not 
generally so distinct as that of gneiss; the cleavage is, however, so much the 
more decided, as is beautifully shown in a quarry of hornblende flag near 
Ruhla in Thuringia. 
Hornblende gneiss occurs more rarely, generally existing near the gneiss, 
and at times even forms independent masses in it. Weiss-stem(Werner) or 
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