292 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



head road the dip is W.N.W. Then for about three miles the dip 

 undergoes frequent changes, owing apparently to the proximity of 

 two dikes of greenstone : then for the distance of more than three 



w. 



Section 2. Glydee Fawr to Bryn-y-ddina 



6 ^ 



N 



^^m...:r^<-<^^^?^f^^!^J^^:r3r^^^^^^>:^*zf^!???c:^^^^^ 



■2 3 2 



The whole series consists of Lower Silurian rocks. 



3. Upper division. 



2. Lower division. 



TT, Greenstone. 

 This section is the continuation east\vard of the section No. 4. 



miles the beds dip with great regularity to the N.E., until you arrive 

 at a mass of greenstone in the centre of Glyder-fawr. This green- 

 stone is seen on the Holyhead road in the ridge which separates Cwm 

 Tryfan from Nant-y-gogo. Beyond the greenstone the dip is W., 

 N.W., or N.N.W., for four miles : beyond the thirty-second mile- 

 stone there are metamorphic rocks and great eruptions of green- 

 stone, and the slates are throw^n into great confusion. 



Overlooking therefore minor local irregularities, there is a syn- 

 clinal axis near the forty-first milestone, at the distance of about Si- 

 miles from the dike, and an anticlinal axis in the centre of Glyder- 

 fawr ; and, consequently, the oldest beds in this section will be found 

 on the north-west flank of the Bryn-y-ddinas dike, and also on the 

 sides of the central axis of Glyder-fawr ; and the newest beds will be 

 found near the synclinal axis, and again on the north-west flank of 

 Glyder-fawr. 



Section 3. The flanks of Snowdox by Rhaidr-cwm to Arenig. 



W. 



3. Lower Silurian series. Upper division. 

 2. Do. Lower division. 



1. Cambrian series, 

 s. Slate. 



TT. Porphyry and Greenstone. 

 The section is a continuation eastwards of that marked (5). 



