198 



SCIENTIFIC NEWS. 



[Aug. 31, 1888. 



oolitic structure, and is exposed on the Gloucestershire 

 side of the Avon, at the entrance to the Gully. We 

 then pass to the Middle Limestone, which extends as a 

 bold line of cliffs up to the hot wells. In this limestone 

 corals, shells, and polyzoa will be found in some beds, 

 but for the most part the rock appears structureless to 

 the naked eye, but a thin section will show it to be 

 full of the remains of microscopic organisms. These 

 largely consist of Foraminifera and a minute organism, 

 averaging about '005 of an inch in diameter, named 

 by Professor Williamson, of Manchester, Calcisplimra. 

 The Foraminifera consists of minute, sometimes many- 

 chambered shells,* filled with a jelly-like, structureless 

 sarcode, in which the most powerful microscopes have 

 failed to detect structure. They occur at the present 

 time in vast multitudes in the calcareous ooze now 

 forming in parts of the Atlantic, and in other seas of 

 lesser depth. As to the exact nature of the Calcisphcerce 

 that at present is a little uncertain. The appearance is 

 that of a minute hollow sphere of carbonate of lime 

 from which spine-like filaments project. In fig. 3 

 these organisms appear like rings, which arises from 

 the hollow spheres being cut in section. 



The Carboniferous Limestone is extensively represented 

 in the Mendip Hills, which extend as a lofty ridge across 

 the northern part of that country. The scenery in the 

 hills is very beautiful, traversed as they are by valley 

 and gorge. The most striking of the latter is the well- 

 known Gorge of Cheddar, situated about twenty-seven 

 miles south-west of Bath, and easily reached by train. 

 There the limestone cliffs rise 420 ft. above the road, 

 crowned by rugged peaks and other grand illustrations of 

 natural rock sculpture. 



The hills are traversed by underground water courses 

 and caves. The stalactite caves of Cheddar have long 

 been famous, and within the last two years others have 

 been discovered by a Mr. Gough. One of these, the 

 " Fissure Cave," is especially instructive, as demonstrating 

 how caves are developed out of fissures. 



The Mendip Hills are also traversed by veins of lead 

 ore, and in past times have been extensively worked. 

 Mr. M'Murtrie, of Radstock, tells us that old records in 

 the hands of the Waldergrave family state that at the 

 time of Edward IV. the lead-mines of the Mendip Hills 

 employed 10,000 miners. 



Passing now to the Coal-measures, we find that within 

 a few miles of Bath there are two coal-fields, namely, 

 the Bristol and Somersetshire. They are regarded as 

 having been once connected with the South Wales Coal- 

 field, and that the separation took place at the close of 

 the Palaeozoic Period, when the strata was folded into 

 anticlinal and cynclinal curves. The anticlinals were 

 raised above the sea-level, and were removed by long- 

 continued denudation, while the cynclinals assumed a 

 basin shape, and were subsequently raised above the 

 sea. 



The Coal-measures of the Bristol Coal-field consist of 

 three series, thus — 



3. Upper Coal-measures .. about 3,000 feet 



2. Pennant Sandstone '. . „ 1,700 „ 



3. Lower Coal-measures . . „ 2,000 „ 



6,700 



The lower series are worked at Ashton,Bedminster, Easton , 

 Kingswood, and Yate. There are twenty-three seams of 



* Scientific News, vol. i., 388, 413, 451. 



coal, which are separated one from another by sand- 

 stones, shales-, and clays. The middle or Pennant Sand- 

 stone series are the least important, and are remarkable 

 for the great development of blue and grey sandstone, 

 known as the " Pennant," which is extensively worked 

 for building and other purposes. Quarries are opened 

 in this rock at Crew's Hole, Fishponds, Downend, and 

 near Warmley, between Bath and Bristol. Plant remains 

 are fairly numerous in this sandstone, and have the 

 advantage of being more durable than those obtained 

 from over seams of coal. They are chiefly Lepido- 

 dendra, Sigillaria, and Calamites. 



There are fifteen seams of coal in the Pennant series, 

 and numerous carbonaceous shales which cannot be 

 called coal, as we understand the term. They yield a 

 red and purple ash, and some contain what for coal is 

 a high percentage of sulphur. They are worked chiefly 

 for house purposes, and only to a limited extent. At 

 Mangotsfield station, between Bath and Bristol, on the 

 Midland Railway, there is a very fine exposure of the 

 Pennant Sandstone with two seams of coal. An exami- 

 nation of this section is especially instructive as demon- 

 strating the conditions under which the seams 

 were formed. Each seam rests on a bed of clay, called 

 the under-clay, and over the top of the coal is a slate, 

 and then come beds of sandstone. Many years ago Sir 

 William Logan pointed out that in the under-clays of 

 South Wales there was to be found a fossil 

 plant named Stigmaria. This fossil was subse- 

 quently discovered to be the root of the fossil 

 tree Sigillaria, and still later of other varieties and 

 allied genera included under the term Lepidodendroid 

 plants. From this fact the inference was drawn that the 

 under-clays were the soils upon which the coal-forming ( 

 plants grew, and that the vegetation was chiefly some 

 form of Lepidodendra or Sigillaria. The exposure of 

 the Pennant Sandstone at Mangotsfield shows that the 

 soil was subject to constant submergence, and on these 

 occasions the vegetation became covered up by sandy 

 debris, which in time became beds of sandstone. Fig. 4 ' 

 is a micro-photograph of a piece of Pennant Sandstone, \ 

 showing it to be made up chiefly of grains of sand 

 which have been cemented together by a siliceous J 

 matrix deposited between the 'grains by percolating water. 



The Somersetshire coal-field may be divided in much 

 the same way as that of Bristol, but there are some 

 seams in the Upper Coal-measures which do not occur in 

 the Bristol area. Mr. J. M'Murtrie,* a well-known 

 authority on the coal-field, gives the following divi- 



Upper Divisions. 

 Pennant Rock. 

 Lower Division. 



/ Radstock Series. 

 \ Farrington Series. 



New Rock Series. 

 Vobster Series. 



From the above it will be seen that the upper series 

 consist of two sub-series, the Radstock, and Farring- 

 ton, making a total thickness of about 2,000 feet. 

 Then follows the Pennant Sandstone, with a thickness of 

 from 2,500 to 3,000 feet, and lastly the lower division 

 including the New Rock and Vobster Series ; the total 

 thickness of the two representing something like 2,800 

 feet of strata. 



(To be continued.) 



* Paper read before the Somersetshire Archaeological and 

 Natural History Society, at Frome, nth August, 1875. 



