118 T. M. EEADE ON THE DEIFT-BEDS OE THE 



Description of Section (fig. 33). 

 Down valley side of trench. 



No. 1. Alluvial gravel and shingle. 



2. Gravel. 



3. Interlaminations of clay, sand, and gravel. 



4. Gravel cemented together with iron oxide. 



5. Shingle and gravel confusedly bedded. 



6. Shingle and gravel, and Tilly matter intermixed with angular, rounded, 

 and well waterworn boulders of considerable size. In places it contains 

 large masses of slaty rock up to 100 tons weight, torn from the valley-bed. 



6a. Similar material at side of valley. 



7. Grey Till. 



8. Blue hard Till containing angular and subangular boulders, mostly of 

 the slaty rock of the valley. It is much more perfectly developed on the 

 sides of the valley than in the bottom of the trench. There are, I 

 believe, in this Till, as well as in Nos. 7 and 6, grits that have come from 

 the mountains at the head of the valley. Some of the stones are 

 scratched and striated, but not nearly so distinctly as those found in 

 the Lo vr -level marine Boulder-clays. 



The opposite side of the trench shows a somewhat different ar- 

 rangement of the preceding beds, due apparently to currents, some 

 of the arched beds of sand and gravel sweeping from near the 

 bottom of the trench to the top. 



"No. 9. Bed rock (summit of Llandeilo) ; a blue slaty rock with no proper 

 cleavage; dip, measured on a plane of bedding 20 feet square, 38° N.W. 

 The beds cross the bottom of the trench diagonally. Huge blocks have 

 been displaced from their beds, and pushed up the plane of the bed below, 

 leaving a cavity at the joint through which a man might walk. The mode 

 in which the rocks have been forced out gives a jagged appearance to the 

 bottom of the trench ; but the angles and asperities have been worn off, 

 and there is a roche moutonnee in the middle. The striations are not 

 very marked ; they run magnetic N. & S. Mr. Deacon informs me that 

 in cutting the trench at the side of the valley for the temporary diversion 

 of the river a mass of rock of 300 tons weight was met with resting upon 

 the rock below and imbedded in drift. 



Cross sections A and B (fig. 33) exhibit accurately the form of 

 the rock surface at the bottom of the trench. Their direction, of 

 course, corresponds with that of the valley, the beds dipping the op- 

 posite way to the slope of the valley. 



Remarks on the Welsh Sections. 

 The effect of the nature of the rocks in each drainage-basin on 

 the character of the drift in the same basin is quite as conspicuous 

 in the examples I have quoted in Wales as it is elsewhere. The 

 sands and clays of Colwyn are evidently derived from the Triassic 

 rocks of the Vale of Clwyd. At Llanfairfechan and Aber the drifts, 

 entirely different from that at Colwyn, are no less clearly traceable 

 to the rocks of the valleys in which they respectively lie, the ar- 

 rangement and size of the boulders and the character of the drift 

 being also affected by the steeper gradients of the mountain-streams 

 and slopes. Near the coast-level the Drift usually partakes more of 

 the character recognized as marine. 



Distribution of the various hinds of Bock-fragments throughout the 

 Drift, and the Light they throw upon it. 

 With the kind assistance of Professor Bonney I have been enabled 



