506 THE GEOLOGIST. 



bourhoods of Llanell}^ Penllergare, and Lloughor. The middle, or 

 Pennant rock series attains its greatest development at Swansea, where 

 it is 3,000 feet in thickness, and presents several important beds of 

 coal ; but in the eastern portion of this field they are very much thinner, 

 and contain little or no workable coal. The summits of the hills which 

 bound the parallel valleys on the north crop, are nearly all capped with 

 this grit, which adds much to the peculiar configuration of the country, 

 and gives a certain identity of outline to its general features. The 

 lower measures are below this rock, and are mostly found on the north 

 crop, where they can be most easily and conveniently studied, both 

 from the gradual inclination of the beds, and the comparatively small 

 amount of disturbance that has taken place amongst them. They are 

 also to be found on the south at Pentyrch, in the Taff Yale, Cefn 

 Cubwr, near Bridge-end, Clive Moor, near Swansea, and Penclawdd in 

 Gower ; but the greater inclination of beds, and the frequent interrup- 

 tions to the series, render them less convenient for the geologist. 

 Having premised this general outline, I will now proceed to offer a 

 few remarks on the fossil remains. As far as I have been able to 

 examine the beds of the upper measures, I have not found anything in 

 them beyond vegetable remains, which are tolerably plentiful ; but no 

 appearance of shells, nor any traces of fish. In the lower measures, 

 however, I have been more fortunate, and have obtained both in con- 

 siderable numbers. The average aggregate thickness of the beds of 

 this series is about forty-seven feet, while that of the respective veins 

 is from two to ten feet. In this accumulation of beds — which, with 

 underclays, seams of iron-ore, sandstones, argillaceous and arenaceous 

 shales, we may roughly compute at fifteen or sixteen thousand feet — we 

 have seven or eight zones of animal life, showing periods when either 

 brackish water or irruptions of the sea prevailed. As, unfortunately, a 

 great difference of nomenclature prevails over the whole basin, and as 

 many seams of coal, called by particular names in one district are called 

 by a very different name in an adjacent locality, I will limit my descrip- 

 tion to one portion of the field, and confine myself to the local names 

 of the north-east crop. 



Passing over the marine forms of the mountain-limestone, we first 

 come to the millstone-grit, which rather thickens in its course from 

 Pontypool to Merthyr. Conformably on this lies a mass of rock of about 

 forty yards thick, known as the Farewell Eock," so called because 



