108 GEOLOGY OF TRICHINOPOLY,, &C. [ChAP. V. 



Foremost among these we must enumerate the great PythoormuUay 

 Pythoormullay group, group^ the secoud of the Vellaur valley series. 



This consists of two main and several smaller branches diverging 

 from each other to the north-west and north-east (roughly speaking) from 

 a spot on the southern slopes of the Pythoor-muUay group. In size these 

 two dykes are about equal, but the eastern branch may preferably be re- 

 garded as the main branch of all, as being of more considerable length, 

 and having a course more generally persistent in one direction. In mi- 

 neral character they are identical, and were probably formed during one 

 and the same volcanic paroxys-m. 



The main branch was traced through the dense jungle between the 

 Patchamullays and Kolymullays, from the Mungumaputty hill north- 

 eastward, with slight variations in its course to within a mile of the 

 Sharvoye hill Trigonometrical-station, a distance of 17 miles. 



The second branch extends from the point of divergence in a north- 

 north-west direction to the banks of the Vellaur river, and is lost sight of 

 in the alluvial bank after a course of 14 miles from the point of 

 divergence. Both branches form ridges of considerable size in various 

 parts of their course, rising from 500 to 1,000 feet and upward, 

 the dark black line of trap rocks showing most conspicuously on 

 the slopes of many of the higher hills they cross, as, for example, the 

 Pythoor hills and the Mulliakurry Trigonometrical-station hill. The 

 branches offer no remarkable features beyond their number and rather 

 strange local distribution. Though of great magnitude, the dykes of 

 this group have no where caused any apparent disturbance of the rocks 

 into which they were injected, hence it seems not unreasonable to conclude 

 that they occupy lines of joint fissures of greater antiquity, because abeady 

 in existence when the volcanic processes were set up by which the basaltic 

 rock reached the surface. In favor of this view of the origin of these 

 dykes is the fact that, at the points of junction of the various branches and 

 cross-dykes, there is no intersection indicative of the dykes belonging 



( 330 ) 



