ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 



475 



Horway, would seem greatly to resemble the above ideal section, 

 if we suppose one half of the same to be obliterated. The follow- 

 ing is a section of the Alleghany chain according to Rogers :* 



4 4 3 4 2 1 



1. Gneiss, mica slate, &c. 



2. Silurian system (so-called metamorphic strata). 



3. Devonian " 



4. Carboniferous " 



The above delineated structure of the slate rocks would have 

 experienced a modification, in the event of igneous rocks having 

 been protruded through the fissures formed by these movements 

 of the earth's crust. These igneous rocks would most easily be 

 protruded at the point marked A in the sketch first above given. 

 If we imagine a granitic mass to be erupted at the point so mark- 

 ed, we have then a section resembling in its general features the 

 build of the so called primitive rocks in many parts of the Alps 

 of Switzerland, in the Saxon Erzgebirge, in Hungary, and in the 

 gneissoid region of La Vendee, above mentioned. The following 

 is a section given by Beudant, of the structure of the schistose 



rocks in the county of Gomor in Hungary .f 

 123435363636 7 6 8 8 8 



1. Granite. 



2. Gneiss. 



3. Mica-schist. 



4. Greenstone. 



5. Limestone. 



6. Clay-slate. 

 1. Iron ore. 



8.' Schistose greywacke and limestone. 



Here the primitive and slate strata rest upon the granite in the 

 following order : 1st gneiss, 2d mica-schist, 3d clav-slate. The 



* Naumann, Lehrbuch, i, 994. 



t Voyage en Hongrie, Atlas, Fig. 5. 



