DOLERITE INTO HORNBLENDE-SCHIST. 143 



To give anj^thing like a critical account of the previous work 

 bearing on the subject would increase the length of this paper to an 

 extent that seems scarcely desirable. I may mention, however, 

 a few facts which show that the point here advanced is by no means 

 new. Dr. Geikie, in his review of Dr. Lehmann's work, in ' Nature,' 

 mentions that Prof. Jukes long ago suggested that many areas of 

 hornblende-rocks may be due to the metamorphosis of basic lavas 

 and tuffs. Mr. Darwin in his ' Geological Observations/ 2nd edit, 

 p. 432, calls attention to the gradual passage from hornblende -slate 

 to greenstone ; but he regards the latter rock as representing the 

 extreme of metamorphism. Mr. Allport, in his valuable paper " On 

 the Metamorphic Rocks surrounding the Land's-End mass of Granite " 

 (Q. J. G. S. vol. xxxii. p. 422), refers to certain greenstones 

 which " might almost be described as hornblende-schists," and in his 

 summary expresses the opinion that "hornblende-schists may be 

 metamorphosed igneous rocks, some being derived from dolerites 

 or gabbros, while others are very probably foliated diorites." 



'' Schistose greenstones " are described by Mr. J. A. Phillips in 

 his two papers '' On the so-called Greenstones of Cornwall " (Q. J. G. S. 

 vol. xxxii. p. 155 and vol. xxxiv. p. 471). Prof. Bonney, in a paper 

 on " The Hornblendic and other Schists of the Lizard District " 

 (Q.J. G. S. vol. xxxix. p. 14), refers to the transition from hornblende- 

 schists to a rock resembling diorite. 



Dr. Lehmann, in his work ' Die Entstehung der altkrystallinischen 

 Schiefergesteine,' describes the passage of gabbro into schistose 

 amphibolite. M. Eenard, M. von Lasaulx, and others hold that the 

 amphibolite schists of the Ardennes have been produced by the 

 mechanical metamorphosis of diorite. Adolf Schenck describes 

 schistose diabase in a paper on " Die Diabase des oberen Ruhrthals," 

 Inaugural Dissertation, Bonn, 1884. 



This account of previous works bearing on the subject is very 

 incomplete, but it is sufficient to show that the conclusions suggested 

 by an examination of the Scourie dykes have been more or less 

 anticipated by many previous writers. 



In concluding this paper, I should like to take the opportunity 

 of acknowledging my indebtedness to Prof. Lapworth. In the 

 summer of 1883 he very kindly conducted Prof. Blake and myself 

 over the Erribol area, and explained to us the very complicated 

 stratigraphy of that interesting region. He called our attention to 

 the secondary structures developed in the rocks by mechanical action, 

 and instructed us where to collect specimens that would best serve 

 for the purpose of microscopic examination. At the time we were 

 on the ground I could not follow him at all points, because the subject 

 was new to me as regards both the stratigraphy and the petro- 

 graphy. Indeed it was not until I had examined the rocks collected 

 under his supervision, as well as others obtained by myself in other 

 regions of the north-west of Scotland, by the aid of the microscope, 

 and had read the work of Dr. Lehmann, published shortly after, that 

 I fully realized the significance of many points that Prof. Lapworth 

 had insisted upon. Although Prof. Lapworth has not seen the 



m2 



