458 PEOCEEDINGS OP THE &E0LOGICAL SOCIETY. 



Brown rock, hard, 4 ft. 6 in. yds. ft. 



Red earth, to 157 



Sandy brown rock, 2 ft. 



Red earth, to 160 



Blue clunch, to 165 



Dark-red hard marl, to 173 



The Keuper escarpment at Compton Dundon is very abrupt ; and 

 the pit was commenced at its base. The beds marked " Lias " at the 

 top of the section are the blue clays of the Ehsetic series. It is thus 

 shown that the boring was continued to a depth of 519 feet, to which 

 is to be added 90 feet for the marls above, giving a total thickness 

 of 609 feet. There is every reason for believing that down to the 

 base of the gypseous beds, and probably in the whole of the strata 

 given in this section, only the Keuper is represented ; and the thick- 

 ness of the Lower ISTew Red Sandstone and anything that may be 

 below can only be conjectured. 



h. Triassic Beds within the Coal-hasin. — In general the actual 

 junction of the New Eed Sandstone with the Carboniferous Limestone, 

 either north or south of the Mendips, is rarely seen, either from its 

 being covered by the Lias, or from a belt of conglomerate intervening. 

 "Within the Coal-basin this formation occupies a considerable super- 

 ficial area, its greatest being at Chew Stoke, south of Dundry, whence 

 it continues for some distance to the west, surmounted by occasional 

 low platforms of Rhsetic and Liassic beds. As compared with the 

 New Eed Sandstone outside the Mendips its thickness is insignificant. 

 The greatest depth it appears anywhere to have attained is at the 

 Tyning Pit, near Eadstock, about the centre of the Coal-measures of 

 the district. It is here 167 feet, and the conglomerate below 19 

 feet. At Norton Hill Pit in the same district the New Eed Marls 

 are reduced to 118 feet; but the conglomerates are 54 feet, on the 

 whole slightly thicker than in the former working. 



c. Batheaston Section. — Another attempt for coal was also made by 

 Mr. William Smith, at Batheaston, in the year 1812, of which I 

 possess a section preserved from that time. This has been given in 

 *' Conybeare and Phillips's Geology of England and Wales," p. 262. 

 In this the beds are divided into 



ft. in. 



Upper Marls (embracing Middle and Lower Lias) 210 



True Lias beds, including White Lias 10 ft., 47 6 



LowerMarls 20 



Immediately following the last deposit, which belongs to the 

 Ehaetic, series, the New Eed Sandstone was included in a thickness of 

 30 feet, and the conglomerate in one of 24 feet. It will thus be seen 

 that vdthin this part of the Somersetshire Coal-basin the Triassic 

 rocks are reduced to a little over 50 feet, whilst south of the Mendips, 

 and where only partially proved, they attain a thickness of 609 feet. 



Notwithstanding the view expressed by Mr. Tawney with reference 

 to the Sutton beds, of which I shall hereafter speak, I am of opi- 

 nion that up to this time there is no evidence in this country of the 

 presence of the St. Cassian and other strata found in the Austrian 

 Alps, which, being supposed to be the marine equivalents of the fresh- 



