488 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 9, 



furrows, which do not reach quite across ; and there is some indica- 

 tion of an obtuse central tubercle. 



Locality (of fig. 6). — Ellergill, near Milbunij Westmoreland. (In 

 the cabinet of Professor Harkness.) 



4. On the Lower Silurian Eocks of the Isle of Man. By Pro- 

 fessor E. Harkness, P.E.S., P.G.S., and Henry Nicholson, Esq. 



The rocks which belong to the lower sedimentary series, and which 

 occupy the largest portion of the surface of the Isle of Man, have 

 been described by Dr. Berger*, and supplemental observations have 

 been made to his memoir by Professor Henslow f. 



The Eev. J". G. Gumming has also given a description of the old 

 rocks of the Isle of Man, with especial reference to the Carboniferous 

 Limestone of the island J. 



The older sedimentary rocks of the Isle of Man are also described 

 in Glover's Guide to this island, which gives a condensed statement 

 of the memoirs of Dr. Berger and Professor Henslow §. 



The natiu-e and arrangement of the old rocks of the Isle of Man 

 are best seen in the coast-sections, which usually occur in the form 

 of bold cliffs. The interior of the island also affords sections in some 

 of the brook-courses ; but the mountains composed of these rocks, 

 which have usually a rounded outline, are covered to a considerable 

 thickness with soil and peat, which hide the rocky masses. 



On the south-east side of the island, in the neighbourhood of 

 Douglas, good exposures of rocks are seen. Along the coast from 

 Douglas to about a mile north-east thereof, the strata appear in the 

 form of thin-bedded grey flags, having the mineral characters of the 

 Skiddaw slate, and dipping south-east at an angle of 60°. These 

 thin-bedded strata, on passing downwards, become thicker-bedded. 

 The rocks here are used for building-purposes, and the finer strata, 

 having a distinct cleavage, are to some extent used for slating. 



The only trace of organic remains here is Palceochorda major, a 

 fossil very abundant in the Skiddaw slates of Cumberland. 

 - A short distance to the north-east, near the village of Onchan, 

 the same thin -bedded Skiddaw slates are seen ; but a little to the 

 south-east of this village rocks of another character, consisting of 

 green slates and porphyries, make their appearance. These green 

 rocks form the headland called Bank's Point, and they are well seen 

 at Crowdale on the east side of it. The green rocks and porphyries 

 which occur here are the equivalents of the ash-beds and porphyries 

 which succeed the Skiddaw slates of the Lake-country. They differ, 

 however, somewhat in their mineral nature from the rocks of the 

 latter country in being more quartzose and in having the ashy rocks 

 better bedded. These green rocks of the Isle of Man have the same 



* Geol. Trans, vol. ii. p. 29 et seq. t Geol. Trans, vol. v. p. 482 et seq. 



X Quart, Journ. Greol. Soc. vol. ii. p. 317 et seq. 



§ The portion on the natural history, including the geology, of the Isle of Man 

 in Grlover's Guide was drjnvn up by the'late Edward Forbes. 



