CLASSIFICATION OF ROCKS. 



53 



remains." But we think we have Vermont granite and mica schist resting on fossilifer- 

 ous limestone. Sir Wm. Logan describes metamorphic strata in Canada of great thickness 

 and extent lying below the fossiliferous, which he calls Huronian ; and below these analo- 

 gous strata, the lowest of all, which he calls Laurentian. These terms, although local, are 

 certainly unobjectionable ; but as to their extent in Vermont we are able to say but little. 

 With so many difficulties to meet we have no ambition to try our hand upon a new 

 classification of rocks, especially the crystalline schists ; for there in fact lies the great 

 difficulty, since all geologists are nearly agreed in regard to the outlines of the great 

 groups. They are also agreed as to the number and character of the particular forma- 

 tions. So that really a diversity of views as to the grouping of some of the highly 

 metamorphic strata is not of much practical consequence. Our chief object in the following 

 outline, which we shall follow, is to avoid the difficulties which we have mentioned ; 

 though in shunning Scylla we may have fallen into Charybdis. The following list con- 

 tains all the well known groups of rocks. 



I. STKATIFIED, OE AQUEOUS BOOKS. 



1. FOSSILIFEROUS. 



a. Cainozoic Period. 



1. Alluvium, embracing Drift. 



2. Tertiary. 



b. Nesozoic Period. 



1. Cretaceous, with Green Sand. 



2. Oolitic, or Jurassic, with Wealden and 



Lias. 



3. Triassic, or New Bed Sandstone. 



c. Palaeozoic Period. 



1. Permian. 



2. Carboniferous. 



3. Devonian. 



4. Upper Silurian. 



5. Lower Silurian. 



6. Cambrian. 



2. UNFOSSILIFEROUS, OR AZOIC. 



1. Clay Slate. 



2. Quartz Rock. 



3. Mica Schist. 



4. Talcose and Chlorite Schist. 



5. Steatite, or Soaps tone. 



6. Serpentine. 



7. Hornblende Schist. 



8. Gneiss. 



9. Crystalline Limestone. 



In this country, as well as in Europe, several of the preceding formations have been 

 subdivided into numerous subordinate groups, and in some cases these lesser divisions are 

 used so frequently that we feel as if it was desirable to give them. This is especially the 



II. UNSTEATIFIED, OR IGNEOUS EOCKS. 



1. GRANITIC. 



1. Granite. 



2. Syenite. 



3. Graphic Granite (Pegmatite.) 



4. Protogine. 



2. TRAPPEAN. 



1. Greenstone, or Diorite. 



2. Tufa, or Greenstone Ash. 



3. Hornblende Rock. 



4. Hypersthene. 



5. Felstone. 



6. Feldspar Porphyry. 



7. Quartziferous Porphyry. 



3. VOLCANIC. 



1. Basalt. 



2. Dolerite. 



3. Amygdaloid. 



4. Peperino. 



5. Trachyte. 



6. Trachytic Porphyry. 



7. Pumice. 



8. Tuff, &c. 



