8 THE LEWIS BROOKS MUSEUM. 



Class 1. — Granitoid Bocks .—This is a class of ternary 

 and binary associations of various minerals, commonly of 

 crystalline structure, and including feldspar as a dominant 

 or distinctive element. It contains specimens of granite, 

 gneiss, syenitic gneiss, &c, &c. In this are included the 

 porphyries, as they contain a base of feldspar. 



Class 2. — Trachytic and Basaltic Bocks. — In this class 

 we find specimens illustrating trachyte, domite, phonolite, 

 basalt, dolerite, melaphyre, &c. 



Class 3. — Volcanic Bocks. — In this class are arranged 

 the various masses, compact and friable, which owe their 

 origin to volcanic eruptions of modern date. It includes 

 lava from various volcanoes, obsidian, pumice, perlite, sco- 

 ria, &c. 



Class 4. — Serpentine Bocks. — In this class are placed 

 serpentine proper and allied rocks, in which occur diallage, 

 and feldspar. Serpentine is illustrated by many beautiful 

 specimens, and we find in addition ophite, hypersthenite, 

 eclogite, &c. 



Class 5. — Amphibolic Bocks. — This includes hornblende 

 (massive), diorite, &c. 



Class 6. — Slates and Schists. — The rocks grouped in 

 this class are chiefly metamorphic and laminated. The 

 class includes mica slate, hornblende slate, clay slate, chlo- 

 rite slate, mica schist, talcose schist, &c, &c. 



Class 7. — Quartz Bocks — This class contains rocks of 

 both igneous and aqueous origin, in which quartz abounds. 

 We find illustrated in it quartzite, chert, arkose, sinter, &c. 



Class 8. — Limestone Bocks. — This includes the rocks in 

 which lime abounds. In it are contained numerous speci- 

 mens of compact limestone, crystalline do., dolomite do. 

 Polished specimens of marble, encrinal limestone, coralline 

 do., lithographic do., chalk, &c, &c. 



Class 9. — Conglomerates and Sandstones. — These are all 

 debris of other rocks in larger or smaller fragments, ce- 

 mented by calcareous, siliceous, or ferruginous matter. In 



