Eeport on the Moel Tnjfaen Drift. 



119 



in Photograph No. 6, of which Fig. 4 is an explanatory diagram : 

 (a) is very stony Boulder-clay, stones mainly of Welsh origin ; 

 {h) yellow loam and sand bedded and contorted ; (c) bedded sand 

 and gravel, 1 foot to 2 feet ; [d] soil 6 inches. The lower edge of 

 the Boulder-clay dips downward into the exposed face rather steeply. 

 BBB are boulders with angular ends projecting from the clay into 

 the sand, the largest being apparently of Penmaenmawr diorite, and 

 the other two of riebeckite ourite of Mynydd Mawr. There is no 

 distinct evidence that the shelly sand and gravel anywhere overlie 

 the Boulder-clay. A close examination showed a distinct line, 

 probably of erosion, between that which passes above and that 

 which passes beneath the Boulder-clay, in which last only were 

 shell fragments found. The sand and gravel above the Boulder-clay 

 may be altogether newer than that in the lower part of the section 

 containing the marine shells, and may possibly be merely hill-wash. 



13. Base of the Drifts and Nature of Underlying Bock Surface 

 (Photographs 7, 8). — The surface of the slate is seen in contact 

 with the sandy group only, the Boulder-clay not reposing directly 

 upon the rock in any part of the section. The surface of the 

 slates is exceedingly shattered, the shattering affecting them to the 

 depth of a foot or two. The shattered edges are, with (o, p. 120) 

 certain local exceptions, bent over in an E.S.E. direction, i.e. to the 

 left of an observer looking along the strike of the cleavage to the 

 S.S.W., the displaced laminae retaining generally their original 

 direction of strike. The displacement usually goes down to the 

 first horizontal joint below the surface, and is a 'displacement' 

 rather than a true curvature. 



These terminally disturbed slates pass up into a band of slate 

 breccia or rubble, composed of angular fragments (e, p. 120). 

 This forms a well-marked band all along the section, and is from 



Fig, 4. — North-west termination of Boulder-clay in Section. 



1 to 3 feet thick. The fragments become smaller towards the top, 

 and have at first a slight inclination upwards to the E.S.E., the 

 upper layers, however, becoming horizontal. Where not obscured 



