m 



ME. H. LAPWORTH ON THE 



[Feb. 1900, 



(2) Corn Gafallt. 



About j mile west of the last section the Gwastaden basement- 

 grits thicken out to some 600 or 700 feet (fig. 7, p. 88) ; and the 

 conglomerate-bed approaches to within an horizontal distance of 

 100 yards or so of the top of the grit-group. 



(3) Allt Goch. 



The Cerig Gwynion Grits may be followed westward for 

 nearly a mile along their line of strike. Their outcrop along 

 •Oorn Gafallt Hill covers a breadth of between 400 and 500 yards ; 



Pig. 8. — Section from Allt Goch towards Tifn-y-graig. 

 NML. Allt Goch S.E. 



s 



3 



' Aa 



[Approximate length = | mile.] 

 Fig. 9. — Section along the Nant-y-Gro. {See p. 93,) 



c N.W. 



% Concrete 

 v *~ Dam 



> f 2 



Footbriclgre 



f,\ ff 



S.E. 



I i Ab t 



i?=:Caban Group. 



[Approximate length = 1 mile.] 



A= Gwastaden Group. 

 Ab = Dy ffrjn Flags. 

 ^46 =Eottenstone Beds 



Ab x = Micaceous Flags and Grits. 

 Aa — Cerig Gwynion Grits. 



x= Blue-black Shales. 

 ff- Faults. 



and if the group be traversed in the direction of the dip, the 

 successive beds may be observed rising in well-marked mounds 

 one after another, suggesting the huge billows of a stormy sea. 

 After crossing the blank formed by the marshy flat of the River 

 Dulas, the grits may be seen sweeping steadily up to the summit of 

 Allt Goch Hill, where they are once more shown in force, resting 

 as usual on the highly-cleaved Blue-black Shales. A section from the 

 highest point towards Ty'n-y-graig (fig. 8) shows the thickness 

 of these grits to be about the same as in our last traverse, but 

 a strike-fault cuts out a portion of this group and the overlying 



