350 Miss I. H. Lowe — Igneous Rocks of Ashprington. 



percentage of common salt. The conditions for successful working 

 on a large scale have been carefully investigated, with a view to 

 controlling the introduction of salt so that the products of 

 volatilization should not be deleterious to the quality of the iron or 

 to the furnace linings. The success of the experiments led to the 

 formation of the British Potash Co., Ltd., forthe commercial recovery 

 of potash from flue-dust supplied by the blast-furnaces of Lincolnshire. 

 It is estimated that the blast-furnaces of the country should be able 

 without difficulty to contribute at least 50,000 tons of potassium 

 chloride per annum, an amount approximately one-half of our 

 pre-war imports of potassium salts. Thus the fear that Britain 

 will ever again experience a shortage of potash as acute as was 

 suffered in 1916-17 is completely dispelled. At the same time it 

 appears to be certain that the country can never be completely self- 

 supporting, unless, perhaps, the dormant exploration 1 of British 

 saline deposits for potash is continued with success. 



II. — The Igneous Bocks of the Ashpeengton Aeea. 



By Miss I. H. Lowe, B.Sc, Demonstrator in Geology, Bedford College, 

 University of London. 



1. Intkoducxion. 



IjS" South Devon the outcrops of Middle Devonian igneous rocks 

 form a series of roughly parallel bands, which broaden out 

 and occupy a continuous area about twelve square miles in extent in 

 the neighbourhood of Ashprington village. No detailed account 

 of the petrological characters of these rocks has been given, 

 although similar types have been described fully in the Plymouth 

 Survey Memoir. For this reason, and also in the hope that further 

 study might explain more completely the cause of the broadened 

 outcrop, I investigated many exposures in the Ashprington area. 



A large number of specimens were collected from this district, 

 a general survey of which showed that the determination of the 

 relations of the rocks to each other over any but limited areas was 

 difficult. This was due to the isolated character of the outcrops, 

 the comparatively rapid change in the rocks exposed, the difficulty 

 of tracing bedding planes owing to ihe development of a marked 

 cleavage, and the absence of sections showing junctions. In con- 

 sequence a more detailed study was made of a small area east of 

 Harbertonford village, covering about two square miles (Fig. 1) 

 This was chosen because there were numerous exposures in a 

 limited space, and the structure is typical of that throughout the 

 district. 



The rocks examined are all basic in composition and strikingly 

 uniform in character, and are either diabases or fragmental basic 

 rocks. Many of the specimens collected cannot be definitely 

 classified owing to the amount of alteration they have undergone. 

 The absence of acid igneous rocks is very noticeable; a rotten 

 felsitic rock from a recess in the road from Gerston Cross to Totnes 

 was the only specimen obtained. 



1 Journ. Soc. Chem. Ind., vol. xxxvii, p. B 313, 1918. 



