Abstracts of Papers read on Geology. 517 



The spaces between the pillows' are occupied by closely -jointed dark- 

 grey chert. The sediments dip to the east at a moderate angle, and 

 probably pertain to the lower part of the Arenig. The pillow lava is 

 finely vesicular and considerably decomposed ; the felspar is oligoclase 

 and forms lath-shaped mici'oliths. Ei'om its structure and mineralogical 

 character the rock is referred to the spilitic suite. 



{d) Careg, near Aberdaron (0. T. Jones). — These rocks have been 

 described in detail by Raisin, and the pillow structure noted as 

 ' spher(iidal structure'. The present notes are intended to supplement 

 that description in certain respects. 



The pillow structure is seen near Careg quarries and near the 

 coast; individual pillows have a length of about 2 feet, and are 

 composed of a fine-grained rock with small vesicles. The felspars 

 have the extinction-angle and refractive index of oligoclase-albite, 

 and are highly charged with decomposition products. These rocks 

 are undoubted spilites, and were claimed as such by Dewey and Flett ; 

 they are associated with ' limestones ' of a peculiar character, together 

 with beds and strings of Jasper, which in places wrap round the 

 pillows in the same manner as the chert near Sam. The association 

 of that rock with a pillow lava may perhaps be regarded as 

 confirming Greenly's suggestion that the jaspers of Anglesey were 

 originally cherts. The associated rocks at Careg have an extraordinarily 

 complicated structure, and probably belong to the pre- Cambrian. 



2. Ckitical Sections of the Cambrian" Area called the Cwms 

 IN the Caeadog-Comlkt IIegion of Shropshire. By E. S. 



COBBOLD, r.G.S. 



rriHE work of excavation of critical sections in the Cambrian rocks 

 X of Shropshire has been continued by the writer at intervals 

 during the past year, and has furnished palseontological proofs of the 

 prolongation of the Lower and Middle Cambrian rocks of Comley into 

 the Cwms area to the south. The sections opened up confirm and 

 amplify those excavated in previous years. 



Excavation No. 53 supplies details of the upper portion of the 

 Wrekin Quartzite and the lowest part of the Lower Comley Sandstone, 

 near the base of which three fossiliferous bands are found, yielding 

 species provisionally referred to Kutorgina, Syolithus, Hyolithellus, 

 and ArchcBocyathiis. 



Excavation No. 54 exhibits a section of the junction of the Middle 

 and Lower Cambrian beds, which is very closely comparable with 

 those of the Quarry llidge at Comley. 



The beds in descending order are as follows : — 



e. Shale with Grit Bands = The Quarry' Eidge Shale, top not ft. 



seen .......... 4 



d. Hard, ringing, glaueonitic Grit = The Quarry Eidge Grit . 28 



c. Conglomerate = The Quarry Eidge Grit, conglomeratic portion 9 

 b. Dark Grey, Purplish, and Eed Limestones = The Black, Grey, 



and Olenellus Limestones of Comley . . . about 4 . 

 a. Green, Micaceous Sandstones, with spotted bands=The 



Lower Comley Sandstone ; base not seen ... 10 



