398 ME. G. H. MORTON ON THE CAEBONIFEROFS [Aug. 1 898, 



The Lower Brown Limestone is mostly of a dark grey, but fre- 

 quently of a red colour, as already described at I^ant-y-Gammer 

 (p. 394), though a considerable portion has been converted into 

 dolomite, which, when weathered, might be easily mistaken for buff 

 or brown sandstone. The lower part of the subdivision is obscured 

 by a deep talus of red earth containing angular fragments of 

 dolomite and limestone, derived principally from the breaking down 

 and decomposition of the dolomite in the cliffs above, so that the 

 exact base is uncertain. It must be, however, a little below the 

 300-foot contour on the 6 -inch map, and consequently much above 

 the base of the Lower Brown Limestone along the outcrop in any 

 of the other hills that have been described. 



The Wenlock Shale beneath is exposed only about the road and 

 railway along the south of the hill, where it dips 45° north-east, 

 and is about 50 feet above Ordnance datum, but probably extends 

 much higher. All the slope of the hill below the overhanging 

 cliffs, about 200 feet, is a talus which covers the steep escarpment 

 of the Wenlock Shale, and the base of Lower Brown Limestone 

 which rests upon it. 



The Purple Sandstone of the Yale of Clwyd appears to be 

 exposed in three localities in the valley east of Eglwys Rhos, the 

 most important being a quarry in a plantation a short distance 

 north-north-east of Bod-y-Sgallen. The colour varies from deep red 

 to yellow, and the red becomes brighter on exposure to the weather. 

 A great quantity of the stone has been used in the neighbourhood, 

 and it is well exposed on the surface of the road leading to the out- 

 buildings west of Bod-y-Sgallen, but the Hall is on the Lower 

 Brown Limestone, In the quarry the dip is only 3° or 4° north, 

 and about 30 feet of the sandstone is exposed. 



There is another exposure on the road at Greengate Covert, as 

 shown by the dip S.S.E. (Millstone Grit) on the Geological Survey 

 map, the other being coloured as limestone. Mr. H. C. Beasley 

 informed me that he had seen the sandstone in the watercourse, 

 i mile to the west, by the side of the road, but the place was so 

 thickly covered with vegetation that I could not find it. 



The relation of the sandstone to the limestone is not shown in 

 any of the exposures, but that it has been let down by faults seems 

 certain, and it probably rests upon the Upper Grey Limestone. The 

 occurrence of limestone at Crogfryn renders it difficult to suggest 

 the position of the boundary-line on the west ; yet there must be 

 faults north and south of the sandstone, which probably extends 

 some distance up the Crenddyn Valley, but how far is uncertain. 



III. Eemaeks on the Dolomite. 



The dolomitization of the Carboniferous Limestone attracted the 

 attention of geologists many years ago, and Prof. PhiUips described 

 the metamorphism of the formation about Kettle weU in Yorkshire.^ 

 The most important paper on the subject is that ' On the Character 



1 ' Geol. of Yorks : pt. ii (1836), Mountain Limestone District,' p. 26. 



