17*) G. A. Cook : 



are filled with an impure limestone, which represents materiaF 

 leached out of the basalt, and deposited in the spaces in the Silurian 

 rocks below. 



Some of this calcareous material has been analysed by Mr. C. E. 

 Crooke in the Agricultural Chemistry School, under Dr. Heber 

 Green. 



The result is as under : — 



CaO =13.82% 



MgO =8.01 



Al.A *» (1 Fe 2 Oa = °- 46 



Soluble Si0. 2 = 0.31 



Insoluble residue = 55. 1 8 



Organic matter and C0 2 (after ignition) = 19.70 



Hygroscopic moisture (1 05°C) = .06 



Alkalies = n.d. 



97.54 



The low summation is probably due to the fact that the alkalies 

 were not determined. Expressed as carbonates the alkaline earths 

 are CaC0 3 = 24.68 ; MgC0 3 = 16.82. Total, 41.50. 



The total expressed as oxides is 21.83. Organic matter is practi- 

 cally absent since the difference between these figures, viz., 19.67, 

 practically agrees with the figures obtained for C0. 2 and organic 

 matter, viz., 19.70. The insoluble residue was obtained by digest- 

 ing the limestone with hydrochloric Acid (strength 182.5 grams per 

 litre). 



Tertiary Dykes. — A dyke very much decomposed and basic in 

 character occurs in the Silurian river cliff South of Bell Street 

 bridge. It is about 1(H) feet away to the West of the axis of an 

 anticline in the Silurian, which anticline strikes a little East of 

 North. The dyke has the same strike, and dips 70 degs. to the 

 West. Its age is probably Tertiary, and it is probably a member 

 of the lamprophyric series of dykes found in other places penetrating 

 the lower Palaeozoic series of Ballarat, Bendigo and Daylesford. 

 At Coburg the relation of the dyke to the Tertiary sands is not 

 clear. li appears, however, to be overlain, both by the newer 

 basalt, and l>\ the outcrop of Tertiary sands, which latter form a 

 -mall outlier South of the Bell Street bridge. This would make the 

 dyke pre newer basaltic, and also pre-Tertiary sands. This would 

 mean that it is connected not with the newer basalts, but with older 

 earth movements, possibly those of the time of the outpouring of the 



