558 Transactions. — Chemistry and Physics. 



which igneous action may be traced, very varying. It seemed, 

 therefore, advisable to take the opportunity afforded by the 

 new Brockley tunnel of studying the influence of the dolerite 

 dyke, through which the tunnel cuts, upon the various strata 

 in its immediate neighboui'hood. 



For position of mine and general geology of district, see 

 " Brockley Coal-mine and Surrounding District," by S. H. 

 Cox, in the " New Zealand Geological Eeports," 1882, page 

 57 : " On Mount Somers and Malvern Hills District," by 

 S. H. Cox, in the "New Zealand Geological Eeports," 

 1883-84, page 33: and "Malvern Hills," by Sir James 

 Hector, in the " New Zealand Geological Eeports," 1870-71, 

 page, 46; and Sir Julius von Haast, in the "New Zea- 

 land Geological Eeports," 1870-71, page 135, and 1871-72, 

 page 46. 



Conditions at Mine. 



Entering the main tunnel, which cuts the dyke nearly at 

 right angles, the following strata are passed in turn, the 

 miners' names being used: (1.) Dolerite, about 300ft. (2.) 

 Fireclay (so-called), 7 ft. 10 m. (3.) Greystone, 5 ft. 7 in. 

 (4.) Plumbago, 4 ft. 6 in. (5.) Anthracite, 2 ft. 6 in. (6.) Or- 

 dinary coal-measures, about 130 ft. (7.) Brown coal, 3 ft. 

 (8.) Measures, 12 ft. (9.) Brown coal, 4 ft. 



At the time of my visit, owing to a fall in the tunnel, no 

 specimens could be taken from the inner end. The brown 

 coal spoken of later was taken from the centre of the 3 ft. 

 seam, where it has been cut by an upper drive. For other 

 specimens I take this opportunity of thanking Mr. Henry 

 Lee, the working manager at the mine. 



1. So-called Fireclay and Greystone. 



These are undoubtedly products of contact-action. It is 

 in the case of argillaceous rocks that we find the greatest 

 variety of products resulting from such action. " When fine- 

 grained siliceous clays are exposed to the action of heat by 

 contact with igneous masses they pass into the hard compact 

 materials often called hornstones, porcellanite.s, &c., and in 

 some of these materials traces of fossils contained in the 

 original rocks may still be detected."''' 



The whitish outer band of porcellanite and the inner grey, 

 or rather blue-grey, stone will probably prove to be but parts 

 of the same stratum. At some distance from the dyke, fossil 

 remains — charred imprints — of the flattened stems or leaves 

 of old vegetation are often to be found. (It is, however, quite 

 possible that the outer portion of the white-clay rock has been 



* Judd's " Lyell " (1896), page 556. 



