514 PEOr. T. G. BONNET ON THE SO-CALLED LIOEITE 



may often be seen in various " spotted schists." Specks of a kaolinized 

 mineral are also present. 



About 500 yards to the south, another but smaller dyke-like mass 

 of dioritic rock cuts the ridge of Long Side ; beyond it is one yet 

 smaller, and oval in shape, and then come three narrow dykes. I 

 visited the second of these; it is an ordinary "greenstone" — 

 probably a hornblendic diabase — rather decomposed. As I did not 

 observe any boulders of the more characteristic picrite scattered 

 above the line of the Little-Knott exposure, I deemed it needless to 

 hunt out the remaining outcrops. 



One point in regard to the boulders from Little Knott is, I think, 

 worthy of notice as bearing on questions other than petrographical. 

 The burn in the ravine below flows over a boulder deposit. This 

 appears to be of some thickness and extends down the glen for a con- 

 siderable distance like a scattered or " trailing " terminal moraine. 

 I followed it for about 300 yards. It seemed to be composed almost 

 wholly of picrite boulders, 3, 4, or even 5 feet in longest* diameter. 

 If then the whole mass corresponds in composition with the part 

 which I saw, the united boulders would form a large mass of picrite 

 rock. Besides this a rather high wall, enclosing a large field on the 

 spur opposite to Little Knott, is almost wholly made up of fragments 

 of the same rock. I think it no exaggeration to say that if all 

 these erratics were replaced on the area mapped as occupied by 

 picrite, the}' would form a conspicuous ridge. In considering the 

 possibihty of Little Knott being the source of the Anglesey boulders, 

 the smaUness of the exposure had always seemed to me a great 

 difficulty, as they are comparatively common in that island. This 

 difiiculty, however, appears of much less account when we view the 

 scattered boulders in the immediate vicinity*. 



This mode of occurrence of the boulders suggests another con- 

 sideration. The mass of boulders in the lower part of the glen has 

 every appearance of a morainic deposit ; but the highest point at 

 which picrite is exposed cannot, I think, be more than 250 feet 

 above the bed of the stream t, and a considerable part of the ridge 

 must have been uncovered in order to allow of so great an accumu- 

 lation of fragments. Hence the glacier can never have been very 

 thick, say not more than 100 feet as a maximum, when it distributed 

 the boulders. As they commence in force immediately below the 

 line of outcrop, it must during the latter part of the time have been 

 very much thinner. It was therefore a local glacier originating 

 under the upper clifFs of Skiddaw and occupying the above-mentioned 

 glen. It follows then that; if boulders have been transported from 

 Little Knott, at any rate to^ the Flintshire coast J, so as to occur 

 in the drift, the only possible explanation is, that the glacier ter- 

 minated in the sea and the boulders were conveyed by floating ice. 



* I believe there is tbe same apparent disproportion between the outcrop of 

 minette on Sale Fell and the boulders distributed thereupon. 



t Little Knott itself is between tbe contour lines of 1000 feet and 1250 feet, 

 probably about 1150 feet ; the dyke in the bed of the glen is on the 900 feet line. 



I As stated by Mr. De Eance, Quart. Journ. Geol. Soc. vol. xxxix. p. 260. 



