THE CAMBRIAN ROCKS NEAR LLASTBERRIS. 765 



them, but the most important feature, the unconformable junction 

 of the Cambrian grits with an underlying series of more ancient 

 rocks, is still plainly visible at a point 75 feet on the Llanberris 

 side of the eighth railway milestone. 



The section published in the ' Geological Magazine ' for March 

 1868, so far as my own observations go, includes two distinct series 

 of rocks — those to the left or south-east (excepting perhaps a few 

 yards at the south-east end of section) consisting of Lower Cam- 

 brian grits with a dip and strike corresponding with the lie of the 

 workable slates of the Glyn Quarries, portions of which are here 

 and there faulted down amongst the grits. Those to the right or 

 north-west end of the cutting consist of a synclinal of brindled 

 slates, banded grits, and conglomerates, which gradually pass into 

 the great mass of grey porphyry-like rock crossing the north-west 

 end of Llyn Padarn. 



Junction of Cambrian Grits resting on Lower Series. 



The nearly vertical lines represent cleavage. 

 The oblique lines the stratification of shales. 



The above figure represents, on a larger scale than that of my 

 general section, the point of junction of the two series, where the 

 obscurely banded Cambrian grits rest unconformably on the edges 

 of an older slate at the south-east end of the synclinal. 



The slates of this lower series differ in character from the work- 

 able slates of the Glyn Quarries, being more shaly, and are brindled 

 with pale bands and patches, less defined than the distinct pale 

 blotches and stripes in the workable slates. 



In both series cleavage and stratification are easily distinguishable, 

 and no possible mistake can be made through confounding them ; 

 indeed the stratification of the lower series is well defined in the 

 alternation of conglomerates and grits with the slates, as well as 

 by the sudden bends and rolls that occur in the banded slates. 



