Yol. 60.] IGNEOUS HOCKS OF PONTESFORD HILL. 451 



with abrupt and steep slopes, but with a general rounded outline. On 

 the north-eastern side it is thickly clothed with fir and larch, while on 

 the south-eastern flank the rocks stand out in bold, bare crags, at the 

 foot of which a thick deposit of coarse screes has accumulated. On 

 the 1-inch map of the Geological Survey the hill is marked as ' green- 

 stone," surrounded by L'ui<jula-Fla.gs, but for a long time rocks other 

 than greenstone have been known to exist in the hill. Murchison, 

 in his ' Silurian System ' 1839 (p. 264), describes the * fine-grained, 

 crystalline, dark-coloured greenstone,' and remarks on the previous 

 page : ' Other veined and altered rocks adhere to the north-eastern 

 face of Pontesford Hill.' 



In 1882 some of the rocks of Pontesford Hill were recognized by 

 Dr. Callaway as belonging to his Uriconian Series. 1 



The resemblance of the banded and spherulitic rhyolites of the 

 northern end of the hill to the Wrekin lavas, especially to the type 

 of Lea Rock near Wrockwardine, is pointed out ; while the pro- 

 nounced flow-lines in the rhyolite are said to 



' dip to the south-south-west at 45°. . . . [The basalt] is apparently intrusive ; aud 

 as it is not found in the neighbouring Cambrian conglomerates it is probably 

 post-Cambrian.' (Op. cit. p. 121.) 



In a synopsis of the microscopic characters of the rocks 

 collected by Dr. Callaway, Prof. Bonney (in an appendix to the 

 same paper) describes a specimen of the nodular rhyolite at the 

 northern end of the hill and of the basalt of the camp at the 

 summit. (These are referred to on pp. 457 and 479 respectively of 

 the present paper.) 



In 1890 the Rev. J. P. Blake, in a paper dealing with the Long- 

 myndian and associated rocks, 2 refers to Pontesford Hill, and says : 



• The igneous portion of the hill consists of two masses of acid rock, everywhere 



separated by a mass of basic rock The whole of the western slope (of 



Habberley Brook), which is formed by Pontesford Hill, is occupied by well- 

 bedded, soft, compact, pale slate, with a moderate dip of about 30° to the west. 

 It is above these slates, on the higher slopes of the hill, that the igneous 

 rocks are met with. On the other, or western, side of the hill only part 

 of the slopes is occupied by a spur of decomposed basic rock ; the rest of 

 the ground between the two masses of acid rock shows numerous exposures of 

 pale slates and grits of varying coarseness, with the usual high dip and strike 

 of the district,' (Op. cit. p. 402.) 



After referring to the section at Lyd's Hole, in which he endeavours 

 to show that the rhyolite there is intrusive in the ' purple slates 

 and grits, which are recognized as Cambrian,' he further says : 

 w On the other, or eastern, side of the hill the slates and grits are 

 of a different character ' (op. cit. p. 403). In the sketch-map 

 accompanying Mr. Blake's paper (pi. xvi) the hill is shown with 



• volcanic acid rocks ' to the north and south, ' higher Cambrian 



1 'The Pre-Cambrian (Archajan) Rocks of Shropshire, Part II, with Notes 

 on the Microscopic Structure of some of the Rocks by Prof. T. Gr. Bonney ' 

 Quart. Journ. Geol. Soc. vol. xxxviii (1882) pp. 119 et seqq. 



2 ' On the Monian & Basal Cambrian Rocks of Shropshire ' Quart. Journ 

 Geol. Soc. vol. xlvi (1890) p. 386. 



