308 



REPORT ON NATIONAL MUSEUM, 1886. 



D.— ROCK CLASSIFICATION. 



The rocks now in use for constructive purposes may be classified suf- 

 ficiently close for present purposes under the following heads : 



A. — Crystalline and Vitreous. 



I. — Simple Rocks. 



1) Silicates : 



(a) Talc (including Steatite ai>d 



Soapstone). 

 (&) Serpentine. (In part.) 



(2) Sulphates: 



(a) Gypsum (including Alabaster 

 and Satin Spar). 



(3) Carbonates: 



(a) Limestone and Dolomites. 



II.— Compound Rocks. 



(1) Massive, with Quartz and Orthoclase; 



acidic: 



(a) Granites and Granite Porphy- 

 ries. 



(&) Quartz Porphyries. 



(c) Liparites. 



(2) Massive, without Quartz: 



(a) Syenite. 



(b) Quartz-free Orthoclase Porphy- 



ries. 



(c) Trachytes and Phonolites. 



(3) PI agioclase rocks; basic: 



(a) Diorites and Diorite Porphy- 



rites. 



(b) Diabases, Gabbros, Mclaphyres, 



and Basalts. 



(c) The Andesites : 



(4) Rocks without feldspars : 



(a) The Peridotites. (Serpentines 

 in part.) 



(5) Schistose or foliated rocks: 



(a) Gneiss (included here with the 



Granites). 



(b) The Schists. 



B. — Fr agmental. 



(a) The Psammites,including Sand- 



stone, Conglomerate, Brec- 

 cia, and Gray wacko. 



(b) Pelites including Clayslates 



and Pipe-clay. 



(c) Volcanic fragmcntal rocks, 



Tuffs. 



(d) Fragmental rocks of organic 



origin (included here under 

 the head of Limestones). 



The order in which the rocks are mentioned above will be adhered to 

 in the descriptions given in the following pages. For the benefit of 

 those not familiar with the order of succession of the various rock for- 

 mations in the earth's crust, the following table is also given : 



