334 Reports and Proceedings — Geological Societt/ of London. 



(lisriiption in tbe same way as the thinner hard bands in the 

 criisli-zones. 



The author contents hinaself with a general account of the 

 Ordovician rocks near Cenmiaes and Portli Wen. He inchides 

 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-Canibriau, 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 quarlzites, and tlie 

 crush-conglomerates. 



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

 (Northern Jersey)." By John Parkinson, Esq., F.G.S. 



In the e!irly pages the general character of this intrusion is 

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

 concludes that only the earlier injections of the intruding granite 

 did tlie work of melting and absorption ; that a latter injection, 

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

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

 o-ranite, now rendered basic through the more or less complete 

 absorption of diabase fragments. 'I'here has been no diffusion of 

 the basic material thus acquired through this second granite. It 

 is pointed out that this explains the intermingling and interstreaking 

 of the two varieties of granite seen on the coast ; the one porphyritic 

 and crowded with fragments, the other non-porphyritic and devoid 

 of fragments. 



Following this general introJuclion, the characters of the granite 

 are described in some detail ; then those of the diabase, formerly 

 an ophitic dolerite. Details of structure of the granite in which 

 absorbed basic material is present, and of the diabase into which 

 acid material has permeated, are dealt with : particular attention 

 bein"- directed to the great alteration which the diabase has under- 

 gone ; this has frequently amounted to a total reconstitution. In 

 this connection are noticed the prevalence of biotite as a product of 

 such mixing and reconstitution when acid material is present in 

 quantity, and the almost entire absence of augite under similar 

 gircumstances. In rocks of heterogeneous origin into which the 

 diabase has largely entered, similar features are described : the 

 presence of nests and veins of acid minerals, the entire loss of 

 ophitic structure, the frequent occurrence of much quartz, and the 

 presence of a mineral believed to be sillimanite. The corrosion and 

 reconstitution of the acid felspars under some circumstances are 

 iio-ured and described ; the earl}' stages of such alterations are 

 touched upon, and a table is given showing the gradual increase in 

 specific gravity with increase of absorbed material. 



In conclusion, points of resemblance and of difference are noted 

 between this district and others ; and an interesting slide from 

 Alderney is described, showing the probable extension of such rocks 

 in other directions. 



