LSS) 
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ie 2) 
W. R. BROWNE. 
NOTE ON THE OCOURRENCE OF CALCITE IN A 
BASALT FROM THE MAITLAND DISTRICT, N.S.W. 
By W. R. BROWNE, D.Sc., 
Lecturer in Geology, University of Sydney. 
With Plate XV. 
[Read before the Royal Society of N. S. Wales, December 6, 1922. ] 
SOME recent petrological investigations by the author in 
regard to the lavas of the Oarboniferous and Permo-Car- 
boniferous systems in the Lower Hunter River district have- 
resulted in the discovery of a number of features of consider- 
able interest. Among other things it has been observed 
that albitization and allied magmatic processes have been 
at work on many of the Carboniferous eruptive rocks, and 
more particularly on the basic rocks which are supposedly 
co-magmatic with these, the amygdaloidal basalts which 
are interbedded with the sediments immediately overlying 
the topmost or glacial stage of the Kuttung division of the 
Carboniferous rocks. 
In these amygdaloidal basalts, whose field-occurrences 
have been described and mapped by Professor Sir Edgeworth: 
David,’ there has been much conversion of basic plagioclase 
into albite, but in addition analcite and another zeolite, 
which appears to be natrolite, commonly take the place of 
the original basic felspar, or even apparently of the replac- 
ing albite. The vesicles are filled with the same Zeolites,, 
and occasionally with calcite and quartz, and in some cases. 
the interstitial spaces between the felspars and other 
minerals in the non-vesicular varieties are occupied by the 
zeolites, which must be regarded as magmatic and primary.. 

4 Geol. Surv. of N.S.W., Memoir No. 4. 
