TRANSACTIONS OF THE SECTIONS. 53 



plain to the north and south. The re-elevation of the Mendip range has occasioned the 

 removal by aqueous denudation of most of the Lias beds deposited on their summit, 

 whilst along the southern flanks of the hills, and in the valley, a considerable thick- 

 ness of this formation still remains in situ. 



Igneous Bocks. — Mr. Charles Moore* has shown that there is an exposure of 

 basaltic rock (dioritic) along the anticlinal of the Mendips, a little west of Dovm- 

 head, extending visibly nearly as far as Beacon Hill, between two and three miles in 

 length and a quarter of a mile in width. 



This igneous mass appears in the form of a dyke, and is coincident with the anti- 

 clinal line along the axis of the Mendips, which is here traceable for seven miles, 

 and is again continued from near Harptree to Shipham. 



There is likewise at the south end of UphiU cutting (Bristol and Exeter Kailway), 

 at the western extremity of Bleadon Hill, an extensive patch of igneous rock, dis- 

 covered when that line was made, and described by Mr. W. Sanders, F.R.S. ; 

 this exposure was also in the line of the anticlinal, and ended in the fault which 

 there crosses the line. This rock, according to Mr. Butley's analysis, is a Pitchstone 

 Porphyry, whilst Mr. David Forbes considers it a Dolerite. 



Whether this dyke was really eruptive or overflowed the Old Red Sandstone is 

 still a question to be solved ; and whether it is coextensive with the range is un- 

 known ; but its age must be subsequent to the Coal Measures — the whole of the 

 Palaeozoic rocks being distm-bed alike, and lying .at one general angle of inclination, 

 the overlying secondary strata not being influenced or at all aflected by these 

 Palreozoic changes. The Old Devonian rocks in contact with the dyke are not 

 altered or metamorphosed, thus establishing the facts of age and condition. 



3. The Radstock District. 



Among the many interesting features of the neighbourhood in which we are 

 assembled is the Bristol Coal-field, which still offers an inexhaustible subject for 

 scientific inquiry — extending from Cromhall in the north to Frome in the south, 

 and from Bath in the east to Nailsea in the west, comprising an area of 238 square 

 miles. 



From a very early date it attracted the attention of geologists, and was long ago 

 the subject of a paper by Mr. Strachey, which was published by one of the local 

 societies. Dr. Bucklandf contributed an able memoir on this Coal-field, in which a 

 great quantity of important information was placed on record, which has been of the 

 greatest possible use down to the present time. 



Subsequently this area has formed the subject of able papers contributed to the 

 North-of-England and South- Wales Institutes of Engineers, by Mr. J. C. Greenwell, 

 F.G.S., and Mr. Handel Cossham, F.G.S., and to other scientific societies by Mr. 

 Robert Etheridge, F.R.S., and IVIi-. Charles Moore, F.G.S. 



During the past twelve j'ears Mr. J. M'Miu'trie, F.G.S. , of Radstock, has been con- 

 tinuously engaged in working out the physical geology of the district, and has con- 

 tributed a series of memoirs on the Bristol Coal-field to the Bath and Somerset- 

 shire Societies, which have thrown a new and important light on those marvellous 

 disturbances which have distorted the strata. 



That part of the Report of the Royal Coal Commission bearing upon the Bristol 

 Coal-field and prepared by Professor Prestwich, and papers by Mr. Horace Wood- 

 ward and Mr. John Anstey, have summarized our previous knowledge, and added 

 recent facts thereto ; but with all that has been done much remains to be investi- 

 gated before a full history of the Bristol Coal-field can be written. 



Although more or less connected throughout, the Coal-fields adj oiuiug Biistol con- 

 sist of three well-defined areas, called the Gloucestershire, Radstock, and NaUsea 

 basins, each of which has its own distinctive features. The Gloucestershire is 

 separated from the Radstock basin by the great KingsM'ood anticlinal, which inter- 

 sects in a ridge-like form the entire Coal-field from east to west ; and the Nailsea 

 basin has been almost, if not entirelj', cut off" from the principal coal district by the 

 elevated limestones of Broadfield Down. Of these three areas Radstock basin is the 



* Quart. Journ. Geol. See. vol. xxiii. p. 452 (18G7).' 

 t Trans. Geol. Soc. 2nd series, vol. i. 



