LAKE ROCKS OF BASIC TYPE. 



is approached, while finally many small crystals of felspar, am 

 sionally quartz, become developed in the purple micaceous base. 



There are a few felstone dykes in the Lake District. One ex- 

 tends from White Pike and crosses part of Matterdale Common. It 

 is thought to be connected with the St. John's quartz felsite. Narrow 

 dykes of banded felstone occur in the south-west of Buttermere. 



Basic Rocks of the Lake District. 



Minette. 1 Professor Bonney describes minettes between Winder- 

 mere and Sedbergh, running east and west in dykes a foot or two 

 wide, typically seen at Cross Haw Beck. The rock is called minette- 

 felsite at Backside Beck, Helm Gill, south of Haygarth, &c. ; mica- 

 diorite at Stile-End Farm ; and kersantite at Holbeck Gill. The dykes 

 are probably of Old Red Sandstone age. The Sale Fell rock, according 

 to Mr. Ward, is a pink felspathic base, consisting of orthoclase and 

 triclinic felspar, generally crystalline. It contains dark green mica, 

 probably biotite, and the quartz, which is interstitial, contains many 

 cavities. 



Diorites of the Lakes. Many small intrusive bosses and dykes of 

 diorite burst through the Skiddaw slates and volcanic series of Borrow- 

 dale. Several occur on the hill-side north of the railway, between 

 Cockermouth and the Bassenthwaite lake. They are generally fine- 

 grained, with white felspar and dark hornblende and specks of iron 

 pyrites. Quartz occurs, with liquid cavities and moving bubbles. 

 Another quartz diorite occurs on the summit and side of Hind Scarth. 

 It contains a good deal of quartz, with many needle-like crystals. 

 Other masses are found at Burtness Comb. The hornblende is a 

 good deal altered, and glass cavities as well as liquid cavities occur 

 in the quartz. A mass of diorite with picrite is seen at Little Knott 

 on the east of Bassenthwaite lake. It is almost entirely formed of 

 hornblende, the quantity of felspar being very small. 



Dolorites or Diorites. Mr. Ward mentions four principal ex- 

 hibitions of dolorite, first at Wythop Fells, a fine-grained dark- 

 green rock, with chlorite replacing much of the plagioclastic felspar. 

 Unlike other diorites, this contains many spaces filled with quartz, 

 which contains many cavities with bubbles. A small mass occurs at 

 Castlehead, Keswick. It is a mixture of pale felspar with augite 

 and a soft dark-green mineral. Most of the augite is replaced by 

 pseudomorphs. Another mass is found at Swirral Edge, Helvellyn. 

 It also has the augite greatly altered and converted into a soft green 

 substance. Across the upper part of Longstrath Valley, Borrowdale, 

 run several dykes, which contain felspar crystals embedded in a fel- 

 spathic base, and mixed with a soft green chloritic mineral. 



We hesitate to group any of these rocks as dolorites, and are 

 inclined from the quartz they contain to regard them as perhaps 

 related to quartz diorites. They may perhaps be connected with the 

 Ennerdale syenite. 



1 Bonney and Houghton, Q. J. G. S., vol. xxxv. p. 165. 



