Yol. 50.] THE GABBRO OF CARROCK FELL. 311 



21. Carrock: Fell: a Study in the Variation of Igneous Rock- 

 Masses. — Part I. The Gabbro. By Alfred Harker, Esq., 

 M.A., F.G.S., Fellow of St. John's College, Cambridge. (Eead 

 May 9th, 1894.) 



[Plates XVI. & XVII.] 



Contents. Page 



1. Introduction 311 



2. Mineralogical Characters of the Gabbro 316 



3. Minor Textural and Mineralogical Variations 319 



4. Orderly Variation from Centre to Margin 320 



5. Discussion of the Causes of such Variation 324 



6. Some Deductions from the Phenomena 329 



7. Reactions between Gabbro and Enclosed Masses of Lava 331 



8. Conclusion 334 



Section across Carrock Fell 314 



1. Introduction. 



During the last two years I have devoted some attention to the 

 igneous rocks of Carrock Fell and the hills west of that well-known 

 summit. Occurring in a somewhat critical situation on the border 

 of the English Lake District, they were examined by Mr. J. E. 

 Marr and myself, partly with reference to their bearing on the 

 general geology of the district ; but, apart from this, they offer in 

 themselves some features which are of sufficient interest to be worthy 

 of record. I have had the advantage of my colleague's co-operation, 

 more especially in the field-work, and take this opportunity of 

 acknowledging my indebtedness to him. 



The earliest connected account of the Carrock Fell rocks was 

 given by the late Mr. Clifton Ward 1 in 1876. He recognized three 

 general types of igneous rocks in the district : — 



(a) Spherulitic felsite of Carrock Fell and Great Lingy ; 

 (6) Diorite (?) of Miton Hill and Round Knott ; 

 (c) Hypersthenite of Mosedale Crags and Langdale. 



He gave a brief account of their characters in the field and under 

 the microscope, with chemical analyses of the first and last, and put 

 forward a view of their mutual relations and mode of origin. In 

 his opinion the several types pass into one another in the field, and 

 he regarded them as produced by the metamorphism of part of the 

 volcanic series, on the strike of which they occur. 



Dr. C. 0. Trechmann, 2 in 1882, pointed out that the dominant 

 pyroxene in the so-called hypersthenite is not hypersthene, but 

 diallage, and the rock would therefore be more correctly described 

 as a gabbro. 



Mr. J. J. H. Teall, 3 in 1885, briefly noticed the spherulitic felsite 

 of Carrock Fell as a typical example of a granophyre in the sense 



1 Quart. Journ. Geol. Soc. vol. sxxii. (1876) pp. 16-27. 



2 Geol. Mag. 1882, pp. 210-212. 



3 Ibid. 1885, p. 109. 



