TRANSACTIONS OF THE SECTIONS. 59 



There are no other rocks in the Isle of Man of an age intermediate between 

 these green rocks and the Old Red Sandstone. 



The dark grey slates and the green rocks, both in mineral character and arrange- 

 ment, represent the Skiddaw slates and the succeeding green slates of the Lake 

 countiy, and an extension of the strike from the Skiddaw country would place the 

 old rocks of the Isle of Man also in the same line. These old rocks of the Isle of 

 Man must therefore be considered as belonging to the Lower Silurian group. 



On the Metamorphic Rocks and Serpentine Marbles of Connemara and Joyce's 

 Country. By Prof. Harkness, F.B.S., F.G.S. 



These rocks, forming a portion of the south-west of Ireland, have on their south 

 side the granitic area of Galway, on the north of which an extensive development 

 of gneissic rocks occurs. These gneissic strata have an east and west strike, and, 

 although greatly contorted, have a prevailing south dip. Coming out from beneath 

 them conformably, is a band of limestone, greyish in colour, and subcrystalline in 

 nature. This limestone, in some localities, is highly serprntinous, and yields the 

 green marble of Connemara. This green marble is most abundant where the lime- 

 scone is highly inclined and greatly contorted. The limestone reposes conformably 

 upon quartz rocks, the latter giving rise to the bold scenery of .Connemara. The 

 mode of arrangement of the metamorphic rocks in this portion of Ireland corre- 

 sponds with that of the Highlands of Scotland ; and these metamorphic rocks of 

 Ireland are the equivalents of the upper quartz rocks, upper limestones, and upper 

 or flaggy gneiss of Sir It. Murchison, being members of the Lower Silurian group. 



It has been stated that the Connemara marble affords Eozoon Canadense, a reputed 

 organism of the Laurentian rocks of Canada. 



The structure in the serpentinous limestone which has given rise to this state- 

 ment, the author believed to be of a purely mineral nature, resulting from asbestos 

 and tremolite which have formed in cavities as crystalline skeletons upon which 

 serpentine has been subsequently deposited. 



On the Pre-Cambrian BocJcs of Central England. 

 By Harvet B. Holl, M.D., F.G.S. 



In this communication the author discussed the age of the crystalline rocks which 

 form the narrow ridge of the Malvems, as also those smaller protrusions which pierce 

 the Cambrian rocks and Keuper marl of Chamwood Forest. In their profoundly 

 altered aspect, in the abundance of triclinic felspar, in the prevalence of hornblende 

 as one of their ingredients, and in their general deficiency in free silica, the rocks 

 in both these localities, though separated by a distance of 60 miles, have neverthe- 

 less a character in common. In the Malvern district they extend for about 8 miles 

 due N. and S., and are again exposed further to the north, near Martley, making 

 altogether nearly 16 miles for the entire length of the known area occupied by these 

 rocks, but nowhere does it exceed f of a mile in width. The dominant trend of the 

 bedding is from S.E. to N.W., i. e. obliquely across the ridge ; hence we learn 

 that the area which these rocks occupy is only an uncovered portion of a much 

 larger one, and it is not possible, therefore, to form an estimate of their thickness, 

 beyond the general one that it is very great. As far as they are exposed, they consist 

 for the most part of alternative belts of micaceous and hornblendic gneiss and schist, 

 the foliation of which corresponds with the plane of the bedding. With these are 

 interstratified belts of coarse, rudely-bedded granite, and of various granitoid and 

 gneissoid rocks, especially towards the northern extremity of the range, with much 

 coarse-grained diorite, and some subordinate beds of crypto-crystalline rock, which 

 have no very definite character. These rocks are traversed by numerous quartzo- 

 felspathic veins, and by trap-dykes (diabase) of later date*. 



In the Chamwood Forest district the rock is more massive, and the bedding for 

 the most part effaced. At Motmt Sorel the rock is entirely granite, and is composed 

 of dark-coloured, ferro-aluminous mica, and a pale pinkish, subtranslucent, triclinic 



* For a fuller description of these rocks, see the author's paper " On the Geologica 

 Structure of the Malvern Hills and adjacent district," in Quart. Journ. Geol. Soc. for Feb 

 1865. 



