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 garnets. Many of the rocks are traversed by 



