Intrusion of Granite into Diabase at Soi'el Point. 31*9 



The following communications were read : — 



1. 'On the Geology of Northern Anglesey.' By C. A. Matley, 

 Esq., B.Sc, E.G.S. ; with an Appendix on the Microscopic Study of 

 some of the Hocks, by Prof. W. W. Watts, M.A., Sec.G.S. 



The strata which occupy the northern part of Anglesey have been 

 the subject of much controversy, some geologists considering them 

 (with the exception of a few patches in the extreme north) to be 

 pre-Cambrian, while others . maintain that they are of Bala age 

 and that they are an upward continuation of the black slates that 

 everywhere appear to underlie them to the south. 



The author attacks this problem from its palaeontological as well 

 as its stratigraphical side. He divides the rocks into three groups, 

 namely : (1) the ' green series,' which forms the floor of the 

 greater part of the area ; (2) the ' northern complex,' occupying 

 a tract along the northern coast and including in it (3) some 

 undoubted Ordovician strata. He adduces palaeontological evidence 

 that the Ordovician rocks lying in the northern complex are mainly 

 if not wholly of Llandeilo age, while the black slates of Central 

 Anglesey appear to range into the Llandovery. The field-evidence 

 shows inter alia that the asserted interstratifications of the Green 

 Series and the southern Ordovician are the deceptive results of 

 thrust-planes which have driven the barren green rocks over the 

 Ordovician beds, the latter being in other places made up of 

 fragments derived both from the Green Series and from the rocks 

 of the northern complex. 



The contortion, overfolding, cleavage, dislocation, and disruption 

 which the rocks have undergone are next described. Disruption 

 is traced from its early stages into ' crush-conglomerates.' Some of 

 the disrupted rocks are Ordovician, and traces of ancient dykes have 

 been found rent to pieces by the movement, which is stated to be 

 post-Ordovician and pre-Carboniferous. The detached masses of 

 limestone and the isolated ' quartz-knobs ' of the northern complex 

 ai'e considered to be portions of strata which have suffered disrup- 

 tion in the same way as the thinner hard bands in the crush-zones. 



The author contents himself with a general account of the 

 Ordovician rocks near Cemmaes and Porth Wen. He includes 

 among them a purple conglomerate and the Orthis Bailyana-beds. 

 Though much inclined to the opinion that the green strata and the 

 northern complex are pre-Cambrian, he admits the possibility of 

 their being of any age up to and including the Arenig. 



The Appendix contains notes on some of the rocks from the 

 Green Series and the Ordovician System, the quartzites, and the 

 crush-conglomerates. 



2. ' On an Intrusion of Granite into Diabase at Sorel Point 

 (Northern Jersey).' By John Parkinson, Esq., E.G.S. 



In the early pages the general character of this intrusion is 

 described. From a consideration of the field-evidence the author 

 concludes that only the earlier injections of the intruding granite 

 did the work of melting and absorption ; that a later injection, 

 probably with no pause, succeeded, taking the same direction as 

 that followed by the first and carried forward with it this earlier 



