1:39 



changes in the sea bottoms, in which this vast accumulation of 

 mineral and organic matter was deposited, may be here studied 

 with much advantage. The entire thickness of the rocks exposed 

 is about 4056 feet ; of this the Millstone Grit is 950 feet, the 

 Carboniferous Limestone 2,338, and the Old Eed Sandstone 768. 



This magnificent section in former years was the subject of 

 several memoirs by Buokland,^ and Conybeaee,^ Bkight,^ and 

 Cumberland. A very detailed examination of it was made by 

 Mr. David WiLiiiAMS, of the Geological Survey, who has carefully 

 described all the beds, and given the chief palseontological 

 features of each. This work is quoted in full in Sir Henry de 

 i/A Beche's admirable essay^ on the formation of the rocks in 

 South Wales and South-western England, to which I must refer 

 the student desirous of more details. 



The lower portion of the series contains Brachiopoda, as 

 Spiriferce, Productoe, and Leptcena depressa, with Encrinites and 

 Corals. The middle portion is not so fossiliferous. The upper 

 division contains gray compact Limestones, with Brachiopoda, 

 and an abundance of Corals. Many of the Coral beds are 

 extremely interesting, from their resemblance to Fringing or 

 Shore reefs of modem times. 



In the Carboniferous Limestone of Ireland, my friend Professor 

 Jtjkes, states that Corals grow to a large size, a foot or two 

 in diameter. In the explanation of sheet 145 of the maps of 

 the Geological Survey of Ireland, Mr. Wynne has figured a 

 LitJiostrotion from Tipperary, which measured 9 feet across. 



''The Corals sometimes occur in beds, a number of species 

 growing together, and forming a regular wide-spread Coral bed, 

 that might be Hkened to a small Fringing or Shore reef. 

 They may, however, perhaps have been deep water species, 

 and at all events there is not the slightest appearance of any 



1 On the South Eastern Coal District of England. Geol. Trans., 2nd series, vol. 1. 



2 Greol. Trans., 1st series, vol. 4. 



' On the Limestone beds of the River Avon, near Bristol. GeoL Trans., 1st 

 series, vol. 5. 

 * Memoir.s of tlie Geological Survey, vol. 1, p. 113. 

 L 



