basalt. The most detailed account is that given by Prof. 

 David, W. F. Smeeth, and J. A. Watt. 1 They described the 

 included boulders of basic plutonic rock as rounded by the 

 corrosion of the molten basalt, and noted the presence of 

 chromite, of chrome diallage, of a green mineral formed by 

 decomposition of chrome diallage, and mentioned the occur- 

 rence of a rock composed of chromite and anorthite — a 

 chromite-anorthosite. Some doubt was thrown on the last 

 determination by the Rev. J. Milne Curran.- Mr. G. W. 

 Card, 1 Dr. H. I. Jensen/ and Mr. C. A. Siissmilch 5 have 

 drawn attention to the widespread occurrence of blocks of 

 plutonic basic rock as xenoliths in intrusions of various 

 types of rocks, more especially basalts. Messrs. Taylor 

 and Mawson note that at Dundas they are sometimes 

 more acid than the basalt including them. 8 Mr. Card has 

 described the basalt of Dundas, which was analysed by 

 Mr. H. P. White. 7 The neck at Hornsby was noted and 

 mapped by the Rev. J. M. Curran and Mr. C. A. Siissmilch, 

 and described by Mr. M. Morrison. 8 Nevertheless no very 

 detailed account of the petrology of these interesting 

 localities lias yet been published. The following is a con- 

 tribution towards such a study. 



Field Geology.-Honisbij.— The volcanic neck of Hornsby 

 is an area about a mile and a quarter long, "the Old Man 

 Valley," lying to the west of the railway station. A 

 geological and topographical map of the neighbourhood is 

 given below. A careful examination of all the exposures 



