262 PROCEEDINGS OF SECTION C. 
1. The first point of resemblance between the diabase- 
capped mountains—the most prominent feature in the 
physical contour of Tasmania—and the laccolitic moun- 
tains of North America, is that they follow none of the 
normal laws of mountain elevation. Thesubterranean forces 
to which they owe their origin did not act like those which 
raised ordinary divides, or which compressed and folded the 
Silurian and older strata along meridional axes, but they 
operated in all directions alike over an area of not less than 
10,000 square miles. 
2. The petrological character of the diabase and its 
remarkable uniformity of type are also strong points of 
resemblance to the somewhat less basic porphyrites of the 
Rocky Mountain region. The structure of both necessarily 
implies deep-seated consolidation of a molten magma. 
3. So far as the evidence goes, the intrusion of the Tas- 
manian diabase and the Rocky Mountain porphyrites 
appears to have occurred on or about the same geological 
horizon. The vast interval in the rock record of Tasmania 
between the Permo-Carboniferous series and the early Ter- 
tiaries may reasonably be regarded as a space once filled by 
a great thickness of accumulated sediments, of which some 
hundreds of feet of Mesozoic coal-measures are the only 
existing representatives. It is among such sediments, -less 
compact than the underlying Permo-Carboniferous rocks, 
that the ascending magmas would naturally spread them- 
selves out along the planes of least resistance under the 
impulse of the forces below. 
4. As to the difficulty presented by the supposed vertical 
dimensions of the Tasmanian mountain-cappings partially 
exposed on eroded cliff-faces, it has been shown that they 
are probably much exaggerated through want of know- 
ledge of the actual position of the line of contact. In any 
case they sink into insignificance beside the recorded thick- 
ness of some of the American laccolites. 
5. The same comparison holds good in regard to the 
removal of the former sedimentary rock-covering; but here 
again it is only the absence of direct evidence that creates 
the difficulty, and it is more than probable that some traces 
of the originally overlying sediments will be found when 
diligently searched for. 
In conclusion I may say that, apart from any interest 
that may attach to it as a geological problem, the subject 
discussed in this paper is one of considerable importance to 
Tasmania, especially as it affects the question of her future 
supply of coal. The acquisition of accurate information 
