TWO NEWLV-DISCOVERF.P WHIN-DYKES 33 1 



yards south of the Collywell dyke, and this will be called the 

 Hartley Dyke.* 



The Whitley Dyke. 



This dyke can be well seen at times, especially after 

 northerly winds, and is traceable almost from the base of the 

 low boulder-clay cliff for 30 yards seawards. At the cliff-end, 

 just above the high-water mark of ordinary tides, it is 14 

 inches broad ; it runs due east for 10 yards, then bends gently 

 to the south, but soon recovers its former direction, and, as it 

 approaches the sea, becomes narrower and split up longi- 

 tudinally by calcite veins. The dyke cuts through thick 

 yellow sandstones which dip inland at a low angle and are 

 jointed in an east-and-west direction ; it makes but little 

 feature, saving what arises from its weathering into rounded 

 blocks, and what is occasionally produced by its erosion below 

 the level of the surrounding rocks, the hardened contact-edges 

 of which stand out somewhat prominently ; and as the 

 weathered surface of the whin closely resembles the sand- 

 stone in colour, it is at times difficult to detect the dyke, even 

 when the rocks are swept clear of sand. 



The freshest rock obtainable from this dyke is soft, of low 

 specific gravity, 2*817, an d contains 7*22 percent, of carbon 

 dioxide— equivalent to 16*4 per cent, of calcium carbonate. f 

 Owing to the state of weathering thus revealed, a complete 

 analysis of the rock was not made. Thin sections examined 

 under the microscope show the rock to be an ordinary basalt 

 about as coarse in grain as the Tynemouth Dyke. The 

 felspars of the groundmass are clear, show binary twinning, 

 and are frequently arranged in star-like clusters. Oxide of 

 iron is fairly developed as an original mineral and largely 

 distributed in a finely divided form as a product of decom- 



* It may be noted that Teall describes the Collywell Dyke under the 

 name of the Hartley Dyke, though locally the dyke always bears the 

 former name. 



t In this, as in all the following analyses, the sample was dried at 

 no° C. 



