276 



REPORTS ON THE STATE OF SCIENCE, ETC. 



Description of the Section. Length of 



trench occupied. 

 h. Rubbly beds of greenish grey sandstone, with clayey partings and 



occasional narrow quartzitic bands . . . . . .13 feet 



g. Glauconitic, coarse-grained quartzite, with a few red grains of 



felsitic material and becoming at the base almost a rotten-stone . 4 feet 

 /. Sandstones and shaly beds, with one narrow band of quartzite . 7 feet 

 e. Compact, grey quartzite ........ 8 feet 



d. Compact, dark grey quartzite, in several beds . . . .10 feet 



c. Blocks of the same bed but broken into angular fragments, and with 



a few referable to higher beds ...... 7 feet 



b. A layer or vein of yellow clay (the fault) ..... — 



a. Red, incoherent sandstone ....... 14 feet 



Remarks : — The gradual change from quartzite to sandstone is paralleled in 

 excavations 4' and 53. ' 2 



The bed g has almost exactly the characters of bed 62 of the latter and portions 

 of a z of the former. 



Section of Tkench in the Cwms, Comley. 



±o Ted' 







Wrekin Quartzite. 



STRIKE 



L^ Comley Sandstone. 



The red incoherent sandstone is strictly comparable with some of the beds of the 

 Torridonian(?) seen in the brook 300 yards W.S.W. of the excavation, and the strike 

 is the same at the two exposures. It seems obvious that though the Cambrian in 

 this section is faulted against the Torridonian( ? ), the two formations are uncon- 

 formable one to another, but the absolute base of the Cambrian has not yet been 

 found. 



Dolgarrog Dam Disaster. — Report of Committee (Dr. E. Greenly, 

 Chairman ; Mr. E. Mont ag, Secretary ; Prof. P. G. H. Boswell, 

 Mr. I. S. Double, Prof. W. G. Fearnsides) appointed to obtain 

 Photographic Records of the Geological Effects of the ' Debacle ' which 

 resulted from the recent bursting of a dam at Dolgarrog, North Wales. 



The Dolgarrog disaster, as a result of which part of the small village of Porth-llwyd 

 was destroyed, occurred during the evening of November 2, 1925. Situated on the 

 western side of the Conway Valley some 6£ miles south of Conway, the village lies at 

 the mouth of the gorge of the Afon Porth-llwyd, one of the small streams draining 

 from the ridge of Carnedd Llewelyn, Foel Fras, and other mountains. The western 

 side of the Conway Valley is hereabouts a steep rock -wall nearly 1,000 feet in height, 

 and above it a mature drift-covered upland rises gently for three or four miles to the 

 mountains, at the foot of which lies Llyri Eigiau at 1,219 feet above O.D. The 

 existence of this lake is determined by a morainic bar which does not lie athwart the 

 valley, but is aligned parallel to the ridge, i.e. north and south. The Afon Porth- 

 llwyd entered and also left the original lake near its southern end. The lake receives 

 the greater part of its water from Cwm Eigiau, the principal eastern cwm of Carnedd 



1 Rep. Brit. Assoc. 1908, Dublin, p. 238 (1909) ; and 1915, Manchester, p. 121 (1916). 



2 Idem 1915, Manchester, p. 118 (1916). 



