310 
FRESH CONTRIBUTION TO OUR KNOWLEDGE OF 
THE CHARACTER AND THE RELATIONSHIP OF 
THE UPPER PALHOZOIC AND MESOZOIC 
FORMATIONS OF TASMANIA WITH THE AS- 
SOCIATED DIABASIC ROCKS. 
By Rosr. M. Jounston, F.L.S. 
(Read April 14, 1885.) 
Recently I have devoted a considerable potion of my time 
to the renewed study of the relation of the prevailing 
diabasic rocks of the Southern portion of Tasmania, for which 
I have also recently had further opportunities afforded me by 
Webster, who most kindly took;me in his yacht Ella to many 
places of interest in the numerous bays, channels, and arms 
of the sea towards the Southern part of the Derwent and 
Huon. 
The relations of the lower marine keds to the diabasic 
ereenstone between Passage Point and Long Bay in the accom- 
panying diagrams unmistakeably show that the greater mass of 
the greenstone, as also shown by the recent bore test at the 
Cascades, is older than the overlying mudstones which quietly 
repose uponit, In one section, however, opposite Half-moon 
Bay, both the older greenstone and the mudstones are 
penetrated by an intrusive sheet of greenstone of later date. 
After abruptly ascending through the older greenstone, the 
later eruptive rock suddenly bends round, and forms a 
horizontal sheet of considerable extent between, and exactly 
parallel to the horizontal bedding of the mudstone and 
limestone series. This is the best example with which I am 
acquainted of the relation of the older and newer intrusive 
rocks with the marine sedimentary formation of upper 
paleozoic age. 
T have also examined carefully the line of country 
between Hobart, Richmond, Constitution Hill, and Spring 
Hill. In many sections between the two latter places, the 
upper coalmeasures repose quietly upon the underlying diabase. 
The best example of this nature occurs in a cutting of the 
main road near Lovely Banks, where the unaltered shales 
and sandstones are seen to repose upon the diabase. The 
only exception noticed by me in this district occurs at the 
head of Spring Hill, where the later intrusive greenstone, 
apparently identical in character with the older, bursts 
through, dislocates, and overspreads certains beds of sand- 
stone, which I believe to belong to the lower part of the coal 
measures. 
At a section immediately beyond Mr. Bisdee’s residence, 
at the foot of Spring Hill, Mr. T. R. Atkinson and myself 
