Geology of Broachueadoivs. 173 



clay and chert bands which traverse the limestone. W. H. 

 Ferguson (12) considers it as probably laid down in a lake 

 occupying a hollow in the glacial conglomerate. R. A. F. 

 Murray (13) judges it to be tertiary in age, and of fresh-water 

 origin, or else a spring deposit. It is reported as hard in some 

 places, soft in others, and in others highly brecciated and mixed 

 with ferruginous clay. It has valuable hydraulic properties, 

 and on comparing the analysis by J. C. Newbery it is seen to 

 contain much less silica and clay than the Broadmeadows stone. 

 A tertiary fresh-water limestone also occurs in the valley of 

 the Duck Ponds Creek. Analyses (15 and 9) show that it is 

 very variable and only magnesian in part. It is noted on the 

 quarter sheet as a limestone which makes good building lime, 

 and may be made into cement when mixed with a proper pro- 

 portion of clay. From a comparison with these rocks one may 

 draw the conclusion that the Broadmeadows rock is too limited 

 in extent and too impure to be ever of much economic import- 

 ance. 



Chemical Characters. 



From the nature of the supposed origin of this limestone, and 

 also from the fact that associated with weathered parts of the 

 newer basalt we often find that magnesite has separated out in 

 hard nodules, we might expect to find great variation in the 

 magnesia percentage. Further, where the limestone has been 

 deposited in the creek we might expect great variation in the 

 amount of material insoluble in acids. Such we do find. 



Specimen No. 39, collected from D, contains about one-third 

 of insoluble material. Specimen No. 38, collected from C, is 

 nmch more uniform in composition, and the insoluble material 

 scarcely amounts to one-sixth. In the rock analysed by J. C. 

 Newbery it is very much less, and only 5.94 per cent. The 

 exact locality from which this specimen was taken is not marked 

 on the quarter sheet, and therefore not precisely known. 



The three analyses agree in a notable quantity of magnesia, 

 and this fact led Professor Skeats to suggest that a thin section 

 should be stained in order to determine whether any dolomite 

 existed. Accordingly thin sections were prepared arid subjected 

 to Lemberg's test. A few drops of a solution of aluminium 



