240 Geology of the Neilgherries. [No. 12, new series. 



which has a conchoidal fracture ; is very sonorous, ringing loudly 

 under the hammer, which rebounds from it. Its green color is 

 derived from the Quartz. By the disappearance of Quartz this 

 stone passes into — 



5th. — Green stone consisting of compact Felspar and Horn- 

 blende. This is known as Whinstone in Scotland. It is of a 

 blackish grey color and one of the most common overlying rocks. 

 Occasionally it has phonolite as a base. It passes into-^ 



6th. — Basalt of which I have observed three varieties, viz. — 

 Compact Felspar and Hornblende, so closely aggregated as to give 

 the rock the appearance of an uniform mass. 



The same ingredients as the preceding, containing dull, crys- 

 tals of Hornblende. 



The same rock, containing brilliant crystals of Hornblende and 

 Augite : the latter recognizable by their pyramidal terminations. 

 These Basalts have a dark blue -grey color. 



The Smaragdite found in the green syenite is a diallage of a 

 fine green color, and pearly lustre in one direction, having a la- 

 mellar structure, and fusing with much difficulty (after hardening 

 into a dark greenish enamel), with borax, into a beautiful amber 

 bead. 



The term Smaragdite to me seems attended with some inconve- 

 nience, inasmuch as this stone may be confounded with the ex- 

 pression " Smaragd" — the German name for the beryl and emerald. 



To return to the amphitheatre, its eastern arm, the peak oppo- 

 site Snowdon, consists of compact granite containing garnets, 

 which I shall hereafter, for a reason previously assigned, denomi- 

 nate garnet rock. 



It is traversed by veins of Quartz, and shelves down almost per- 

 pendicularly from the summit, in escarpes to the north and east. 



Between this peak and the north flank of Dodabett, the garnet 

 is found in great abundance in rocks protruding through the sur- 

 face, in detached blocks of red compact granite which affect the 

 Dodecahedral form, the primary crystal of the garnet, and in a 

 conglomerate. The surface of the ground is actually reddened 

 from comminuted garnet*. Many of the rocks are traversed by 



