BY W. G. WOOLNOUGH. 



791 



small patches of similar slaty rocks completely detached from the 

 main area, and isolated from it by bands of eruptive rock. The 

 largest of these isolated masses occurring near the Marulan 

 Show Ground is nearly 500 yards in length, and, from this,, 

 pieces down to less than one inch in diameter can be traced. 

 The smaller pieces are certainly "Daly-masses," fragments stoped 

 off from the roof of the magma-chamber during the closing 

 periods of active intrusion. It is difficult to conceive that a 

 mass as large as the slate-area on which Barber's Trig, lies could 

 have been stoped off in this way. The form of the boundary 

 between it and the grano-diorite suggests a different explanation. 

 The junction-line nearly follows the contour of the ground-surface,, 

 showing that the surface of contact is an almost horizontal plane; 

 and I suggest that we have here the last undenuded remnant of 

 the roof of a laccolite or hatholith. The eruptive material has 

 been bared by denudation quite recently (geologically speaking} 

 and we should expect to find the phenomena described by Daly.* 

 As a matter of fact, the grano-diorite is full of angular slaty 

 fragments, even at distances of a mile and a half from the present 

 contact; it is probable, however, that the distances of such 

 points from the original roof is much less (see text-fig.) 



Sketch-section to show probable original form of the plutonic 

 mass, and especially its flat upper surface. 



To summarise, then, we have a long, rather narrow, band of 

 coarse plutonic rock, trending in a meridional direction, intrusive 

 into the sediments whose strike is in the same general direction. 



* Daly, R. J., Amer. Journal of Science, 1903. 



