634- REPORT — 1901. 



y. Oii tha Alieratioits of the Lias Shale hi/ the Whiii Dyke of Great 

 Aijton, in Yorkshire. By George Barrow. 



[Communicated by permission of the Director of the Geological Survey.] 



The examiuation of the least altered portion of the rocks of the Highland 

 series in the area between Blairgowrie (Bridge of Cally) and Stonehaven has 

 8ho^vn that the grits are composed of practically unaltered grains or small pebbles 

 of quartz and oligoclase i'elspar set in a matrix of an iinusiial character, and 

 difficult to understand, as all traces of clastic micas have been obliterated from 

 it. It occurred to the author that this was due to heat action, and to test tliis 

 point slices of baked Lias shale were prepared, the specimens being taken from 

 the edge of the well-known Cleveland Dyke at Great Ayton. At six inches 

 from the edge of the dyke the clastic micas are large and abundant, but at the 

 contact they are entirely digested, and material like the matrix of the Highland 

 grit is produced. The minute pebbles are not affected in any way, and retain 

 their original form, size, and optical properties. It is thus shown that in 

 entering the Highland area we begin with rocks which, though little altered, owe 

 that alteration entirely to heat action. 



10. On Cairnyorins- By E. H. Cunningham Ceakj, B.A. 



The search for these crystals was formerly a very profitable industry in the 

 districts contiguous to the great granite musses, but it has now been practically 

 abandoned. The cairngorms were obtained loy digging shallow pits and trenches 

 in the decomposed granite and debris which covers most of the Hat hill-tops, and also 

 appears in many of the corries. The presence of vein-quartz, muscovite, large crystals 

 of orthoclase and graphic intergrowths of quartz and felspar in the loose debris have 

 been recognised as indications of the existence of the cairngorm-bearing veins. 

 Examination of the cliff sections in the deep corries reveals the presence of vertical 

 or highly inclined veins of line granite intruded in the coarser surrounding rock. 

 These veins are more acid than the normal granite, and contain drusy central zones 

 in which the crystallisation is coarse. These central zones are characterised by 

 the presence of graphic intergrowths, muscovite plates, and, where the druses are 

 sufficiently large, idiomorphic crystals of orthoclase and more or less smoky quartz. 



Beryl is also present in some cases. 



These idiomorphic quartzes are the cairngorms, but are only valuable when 

 large and well coloured. 



The veins probably represent the intrusion of more highly differentiated 

 material from the underlying magma into fissures due to contraction on cooling, 

 while the druses have probably a similar origin, and have been filled with highly 

 acid solutions from which the crystallisation took place. 



11. Oti the Circulatioii of Salt and its Geoloyical Bearinya} 

 By William Ackroyd, F.I.C, Public Analyst for Halifax. 



During storms salt is driven from the sea far on to the land, is dissolved by 

 rains and carried back to the sea ; in calm times the phenomenon is also in progress. 

 Various computations have been made of the amount of salt deposited on the land 

 in this manner from 24*r)0 lb. per acre per year at Rothamsted to B41 lb. at 

 Pennicuick. The writer estimates that during 1900-1901 there wasl7l'-o lb. per 

 acre per year deposited on the Pennine Hills, nearly midway between the Irish Sea 

 and the German Ocean, at an altitude of over 1,000 feet above sea-level." 



It is shown that for the Millstone Grit and the limestone districts of Yorkshire, 



' Published in full in the Geological Magazine, December \, vol. viii. p. 445, 

 October 1901. 



- Ackroyd, 'Researches on Moorland Waters,' Pt. II., Journ. Cliem. S(.)c.,\o\. xxix. 

 p. 674. 



