CCURRENCE OF GASTRIOCERAS AT IRWIN RIVER COALFIELD 249 
NOTES on rHE OCCURRENCE or GASTRIOCERAS at 
THE IRWIN RIVER COAL-FIELD, W.A. 
AND A COMPARISON WITH THE SO-CALLED PARALEGOCERAS 
FROM LETTI, DUTCH EAST INDIES. 
By W.8. Dun and Prof. Sir HDGEWoRTH DAVID, K.B.E., 
C.M.G., D.S.0., D.Sc., F.R.S. 
[With Plates XI - XIII and Text Figures. | 
[Read before the Royal Society of N. S. Wales, December 6, 1922. | 
THE late R. Htheridge Jnr. described a large ammonoid? 
found by the Geological Survey of West Australia in the 
Irwin River Coal-field, under the name of Gastrioceras 
Jacksoni, in the year 1907. 
In a recent examination of the Irwin River Ceal-field by 
Dr. W. G. Woolnough, and a still later reconnaissance by 
Mr. A. Gibb Maitland and Professor David in the same area, 
it was ascertained that the horizon for Gastrioceras : 
estimated by Dr. Woolnough was some 1600 feet above the 
basal tillites of the field, and over 5000 feet below the. 
horizon of the Irwin River Coal Measures. Diamond drill 
bores last year proved that marine strata with numerous. 
Aviculopecten etc. overlie these coal measures and are 
therefore probably the equivalent of the Upper Marine 
series of the Hunter River district. The Irwin coal 
measures in this case become the probable equivalents of 
the Greta Coal Measures of New South Wales. Hence the 
horizon for Gastrioceras is far down in the equivalent of 
the Lower Marine series of the Hunter River district. It 
is therefore a matter of great stratigraphical importance 
to determine the approximate horizon of this Gastrioceras 
of the Irwin Coal-field in reference to its place in the 
Tethyan fauna of the Dutch Wast Indies; and as the 
* Bull. Geol. Surv. W. Austr., No. 27, p. 36, pl. 9, f. L=38. 
