308 



REPORT ON NATIONAL MUSEUM, 1886. 



D.— ROCK CLASSIFICATION. 



The rocks now iu use for constructive i)iirposes may be classified suf- 

 ficiently close for present i)urposes under the following heads : 



A. — Crystalline and Vitreous. 



I. — Simple Hocks. 



1) Silicates : 



(a) Talc (iucluding Steatite ai'd 



Soapstofte). 

 {b) Serpentine. (Iu part.) 



(2) Sulphates: 



(a) Gypsum (iucluding Alabaster 

 and Satiu Spar). 



(3) Carlionates: 



(a) Limestone and Dolomites. 



II. — Compound Rocks. 



(1) Massive, witli Quartz and Ortlioclaso; 



acidic: 

 (a) Granites and Granite Pori>hy- 



riea. 

 (6) Quartz Poriihyries. 

 (c) Liparites. 



(2) Massive, without Quartz : 



(a) Syenite. 



(Z») Quartz-free Orthoclaso Porphy- 

 ries, 

 (c) Trachytes and Phonolites. 



(;i) PI agioclase rocks; basic: 



(o) Diorites and Diorite Porphy- 



rites. 

 (&) Diabases, Gabbros, Mclaphyres, 



aud 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). 

 {h) The'Schists. 



B. — FltAGMENTAL. 



(a) The Psami*iite8,including Sand- 

 stone, Conglomerate, Brec- 

 cia, and Graywacke. 



(Z>) Pelites iucluding Clayslates 

 aud Pii)e-clay. 



(c) Tolcauio fragniental rocks, 

 Tufls. 



{d) Fragmental rocks of organic 

 origin (included here under 

 the head of Liraestoues). 



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

 iu 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 : 



