01? THE SO-CALLED DIOKITE OE LIITLE Kly'OTT. 511 



37. On the so-called Diokite of Little Knott (Cumberland), ivith 



further remarJcs on the Occtjreence of Picrites in Wales. By 



Professor T. G. Bonnet, D.Sc, LL.D., P.E.S., Pres. G.S., 



Pellow of St. John's College, Cambridge. (Read May 27, 



1885.) 



[Plate XYI.] 



In my second note * on the hornblende-picrite boulders which are 

 scattered over the neighbourhood of Ty Croes, Anglesey, I briefly 

 noticed a similar rock which occurs in situ at Little Knott in the 

 Lake District, and has been described by the late Mr. Clifton Ward 

 as an exceptional variety of diorite. In the spring of last year I 

 was enabled to visit this district, and had the advantage of the com- 

 pany of Mr. J. Postlethwaite of Keswick, whose local knowledge 

 was of great assistance to me. Little Knott is a slight prominence or 

 shoidder on the crest of Long Side, a spur from the main mass of 

 Skiddaw, where the former begins to fall more sharply down to the 

 lowlands on the north. The picrite is represented on the six-inch 

 map of the Geological Survey as an elongated dyke-like mass, running 

 nearly E. and W. for about 650 yards, and generally about 40 yards 

 wide, the outcrop of which extends from Little Knott across a ravine 

 to a point at about the same elevation on the opposite ridge. The 

 boundary, however, is inferential in a part of this area, as the rock 

 is by no means continuously exposed, no small portion being covered 

 with turf. 



Long Side consists of Skiddaw Slate ; at one locality on its western 

 slope Graptolites are not rare, and here Mr. Postlethwaite on the 

 occasion of our visit discovered a Lingula. At Little Knott itself the 

 picrite mass, being about its usual width, is bounded on either side 

 by a low outcrop of indurated Skiddaw Slate. Prom this part of the 

 crest the picrite can be traced eastwards down the steep slope ; an 

 irregularly projecting mass, traversed by occasional joints, and thus 

 divided into large blocks, giving to the greater prominences quite a 

 grandiose aspect. It foUows the line of a slight depression and is 

 ultimately covered up by the turf. The burn at the bottom of the 

 glen runs over a mass of boulders. On the opposite hillside no 

 rock was visible above the turf until we reached about the level of 

 Little Knott, where, on the brow of the ridge, is a group of huge 

 blocks. I could not satisfy myself that any of these were certainlj^ 

 in situ, though the live rock must be close at hand. Mr. Ward, I find, 

 regarded them as boulders. The largest block is about 18 feet long, 

 8 feet wide, and 7 feet high : it rests on Skiddaw Slate, which has a 

 baked aspect and appears to be in situ. A short distance to the 

 south, among indurated Skiddaw Slate, is an outcrop which Mr. Ward 



* Quart. Journ. Geol. See. vol. xxxix. p. 254. I may take this opportunity 

 of correcting a misprint : on p. 265, line 8, for milky read silky. 



Q.J.G.S. No. 164. 2o 



