TWO NEWLY-DISCOVERED WHIN-DYKES 34 1 



analyses of the fresh rock and the weathered (underground) 

 top and bottom of the sill show considerable extraction of 

 lime, and to a less extent of other bases, and conversion of 

 the residual bases almost entirely into carbonates. It is 

 possible, though by no means certain, that the weathering 

 agent in this case has been carbonic acid. 



The weathering of the Cleveland Dyke has been studied to 

 some extent by Teall and others* and two radically different 

 types established, namely, carbonation and kaolinisation. 

 Teall has further investigated (op. cit.) an interesting case in 

 that of the Highgreen Dyke, where solution and precipitation 

 have taken place concurrently, the result being the production 

 of a cellular structure, the bases being removed from the 

 insides of the cells and the iron precipitated along the cell- 

 walls. 



In conclusion, emphasis may be laid on the similarity of 

 the Hartley Dyke to the Collywell and Crookdene Dykes. A 

 considerable amount of evidence has already been given in 

 support of the view that the two last-named dykes are 

 different exposures of the same intrusion {see " The Dyke at 

 Crookdene, etc.," p. 12); and the results of the study of the 

 Hartley Dyke, embodied in this paper, lead to the conclusion 

 that this dyke is intimately connected with and possibly an 

 offshoot of this intrusion. The Whitley Dyke has evidently 

 affinities to the Tynemouth Dyke; a thorough petrological 

 examination of the two rocks will probably bring these into 

 clearer light. 



* J. J. H. Teall, " Petrological Notes on some North of England 

 Dykes," Quart. Journ. Geol. Soc, 40 (1884), p. 209. 



Stanley Smith, "The Cleveland Dyke," Proc. Univ. Durham Phil. 

 Soc, vol. 2 (1906), pp. 239-242. 



