Il8 OLD RED SANDSTONE. 



the Sandstone group : for these higher beds of the sandstone 

 stretch across the Silurian outcrops westwards on to the older rocks 

 near Caermarthen. 



That the Old Red Sandstone of this country comprises in reality 

 only two divisions is now the opinion most usually held. Prof. 

 Hughes, in 1875, suggested a twofold classification of the beds. 

 Those which followed the Silurian without a break he termed the 

 Sawdde beds, from the river Sawdde, a tributary of the Towy, which 

 joins that river south of Llangadock in Caermarthenshire, along 

 which the best continuous section is seen. The Upper Old Red 

 Sandstone is here represented by the quartz-conglomerates "which 

 rest upon the Sawdde beds and underlie the brown sandstones of 

 the Vans. This upper division may be regarded as the variable 

 basement-series of the Carboniferous, and the equivalent of the 

 thin conglomerates, etc., known as the Old Red Sandstone or 

 Conglomerate in North Wales and in the North of England.^ 



The section in the Sawdde valley attracted the attention of De la 

 Beche during the progress of the Geological Survey, for as he 

 remarks, "Some embarrassment was experienced as to a really good 

 line of demarcation between the Silurian rocks and Old Red Sand- 

 stone in South Wales and Herefordshire." ^ 



That the Old Red Sandstone was essentially a deposit 

 formed in large lacustrine areas is a view originally suggested 

 by Dr. John Fleming. The subject was discussed by Mr. 

 Godwin-Austen,^ and has more recently been elaborated by 

 Dr. A. Geikie in describing the limits of the old 'Welsh 

 Lake.'^ Whether the lacustrine areas were entirely fresh- 

 water may be open to question, for the organic remains of 

 the Lower Old Red Sandstone had, many of them, lived on 

 from Silurian times. It is, however, quite possible that the 

 lacustrine area in which the Lower Old Red Sandstone was 

 formed may have been originally part of the open sea, subse- 

 quently isolated like the Caspian.^ 



Until the beds are mapped out in further detail, it is not 

 possible to define the boundary between the Upper and Lower 

 Old Red Sandstone, nor to indicate the areas over which they 

 were respectively deposited. The Rev. J. C. Ward expressed 

 the opinion that there may have been glaciers in 'Old Red' 

 times, which scooped out the lakes.*" 



^ Brit. Assoc. 1875, Sections, p. 70 ; Q. J. xxxviii. 209. 



^ Mem. Geol. Surv. vol. i. pp. 23, 46, 69. 



^ Q. J. xii. 51. * Trans. Roy. Soc. Edin. xxviii. 346. 



^ See Ramsay, Physical Geology and Geography of Great Britain, edit. 5, 

 p. 106. 



'^ G. Mag. 1S70, p. 15. See also Hughes, Geol. and Polyt. Soc. W. Riding, 

 1S67. 



