THE NEIGHBOURHOOD OF BANGOR. 483 



drewen pit *. It does not, however, appear to me that the quartz 

 and jasper grit and conglomerate west of the pier at Garth can be 

 associated with the above. The following extract from my note- 

 book explains the sequence of the rocks on this part of the shore : — 

 " W. of the new slate-pier are dark beds, resembling in the upper 

 part those on the other side of the pier mapped as Arenig, and in 

 the lower becoming gritty and containing bands of small pebbles only 

 a few inches thick, the general dip being 10°-20° S.E. Then we 

 come to green and purple bastard slates, faulted down, and in places 

 much disturbed in consequence, the prevalent dip (not easy to ascer- 

 tain) being apparently 40° S.W. Just west of the old slate-pier is 

 a bank of screes of bastard slate and fine grit, among which I found 

 bits of green breccia, reminding me of those seen above Bryniau, 

 though in a much finer condition. About 150 yards east of the 

 bathing-place green-bauded argillites dip at about 40° S.E., and 

 slaty beds then continue to the bathing-house, when the conglo- 

 merate sets in, which, so far as one can ascertain, has an easterly 

 dip." If these observations are correct, it is evident the whole 

 district is completely smashed up by faults. 



I have, however, found a rock, seemingly just on the north side of 

 the main fault in the Caernarvon-road valley (in a quarry north of 

 the crossing of the road from Maesmawr to Brithdir), bearing some 

 resemblance macroscopically and microscopically to that at Tair- 

 ffynnon ; and in a pit at the back of Caemabadden Farm is a greenish 

 grit, which, in its coarser parts, contains bits of green slate and red 

 felsite, and may belong to the upper part of the zone between B and C. 

 If I am correct in the position I assign to the bed A, then the whole 

 series north of the fault has a strike rather to the east of N.N.E. ; 

 so that all the upper part of the Bangor series would be cut out by 

 the faults which bring down the very Cambrian-looking beds above 

 the cross roads at Pen-y-chwintain. 



Until the outcrops can be laid down on a map on the 6-inch 

 scale, it will be hopeless to come to any satisfactory conclusion in 

 this complicated district north of the fault, and not easy to bring 

 into complete order that on the southern side. I trust, however, 

 that I have succeeded in showing that my original reading is the 

 more simple explanation of the facts observed both in the field and 

 with the microscope — namely, that there is a general ascending suc- 

 cession in this district, and that under the name of the Bangor 

 Beds we must include not only the green gritty slates and breccias 

 assigned to them by Professor Hughes, but also a large lower group 

 extending from A to a little above C. This group has probably 

 derived much of its material from the denudation of the great 

 masses of rhyolitic lava to the south-west, and the lapilli which are 

 often present may have been derived from its associated cones. At 

 the same time, seeing that these lavas appear generally to rest upon 

 old gneissic and granitoid rock, the slaty fragments, often very 



* Which would be lithologically the least difficult, -were not this grit ap 

 parently so completely " sandwiched " between the Bangor grits and breccias 

 and the Cae-Seri breccia. 



