Minerals of Granitic Rocks of the Lake District. 415 



At Goblin Combe, as the result of digging nearly forty trial- 

 holes, it was ascertained that the igneous rocks form two discon- 

 tinuous, somewhat crescentic masses, each consisting of olivine- 

 basalt overlain by a considerable thickness of calcareous tuff. 

 At Uphill, the evidence obtained was insufficient to determine 

 whether the basalt is a sill or a lava-flow. At Limeridge Wood, 

 Tickenham, where only debris of basalt had previously been 

 recorded, the presence of an oval mass measuring about 60 by 

 25 yards was proved by digging trial-holes, and the fact that it is 

 completely surrounded hj limestone indicates its intrusive character. 

 Several additional exposures are described on Milton Hill, where 

 the lava forms a band about 150 feet thick. The lava of Middle 

 Hope or Woodspring is shown to form an irregular and discon- 

 tinuous mass. 



Previous statements as to the essentially basaltic character of 

 these rocks are confirmed. Olivine is present at each locality. 

 Analyses, mainly made by Mr. E. G. Eadley, show that in some 

 of the rocks a high percentage of potash is present. 



June 9th.— Dr. A. Smith Woodward, F.K.S., President, 

 in the Chair. 



The following communications were read: — 



1. ' The Accessory Minerals of the Granitic Rocks of the English 

 Lake District.' By E. H. Rastall, M.A., F.G.S., and W. H. 

 Wilcockson, B.A. 



The work described in this paper arose out of independent researches 

 on the mineral composition of sediments, in which it became desirable 

 to study the genesis of certain minerals. Preliminary investigations 

 promised results of interest if the rocks of a whole district were 

 examined, and for this purpose the Lake District was selected. 

 The rocks here described are the granites of Skiddaw, Shap, and 

 Eskdale, the microgranite of Threlkeld, and the granophyre of 

 Buttermere and Ennerdale. 



The material was pounded in a mortar, washed and panned, and 

 the concentrate separated in bromoform after the removal of the 

 magnetic portion. 



The general results showed a well-marked variation of accessory 

 minerals between the different intrusions, but a similarity between 

 parts of the same intrusion, although the minerals of apophyses are 

 not always the same as those of the main mass. No evidence is 

 afforded for a genetic connexion between the different intrusions. 



One of the most remarkable results obtained is the rarity of 

 magnetite and the wide prevalence of pyrrhotite. which was present 

 in every sample examined, some thirty in number. Special atten- 

 tion was paid to the characteristics of the zircon-crystals, which 



