34 



testimony to the value of Mr. Symonds' remarks. It is made up of water-worn 

 pebbles, vein quartz, jasper, &c., which were embedded in the sediment of a 

 turbid ocean, and it is a subject for enquiry whence those rounded pebbles were 

 derived. Like the stalagmite just spoken of, the siliceous veins, of which the 

 pebbles are the remaining fragments, were evidently formed in fissures and 

 crevices of sedimentary rocks, but of a still more ancient system, which had been 

 broken up ere its constituents were washed into the Devonian seas. Many of the 

 pebbles were observed to have portions of the ancient rock still adhering to them. 



Under the guidance of Mr. Strickland, a number of the party proceeded 

 southwards from Symond's Yat to the coal-pits at Christchurch. On their way 

 thither he pointed out the outcrop of Millstone-Grit which forms the inner edge 

 of the Coal basin. The structure and organisms of this formation lead to the con- 

 clusion that it was deposited in a shallowing sea in the vicinity of land, and that 

 it subsequently received a deposit of muddy sediment destined to become the soil, 

 whence should spring up a vegetation far surpassing in luxuriance that of the 

 most favoured tropical spots of the present day. Geologists are, however, not 

 agreed as to the precise circumstances under which the vast accumulation of 

 vegetable matter took place to produce the phenomena of the Coal Measures. 

 The most prevalent opinion cannot be better explained than in the words of 

 Sir C'harles Lyell : — 



" The beds throughout, with the exception of the coal itself, appear to have 

 been formed in water of moderate depth, during a slow, but perhaps intermittent 

 depression of the ground, in a region to which rivers were bringing a never-failing 

 supply of muddy sediment and sand. The same area was sometimes covered 

 with vast forests, such as are seen in the deltas of great rivers in warm climates, 

 which are liable to be submerged beneath fresh or salt water should the ground 

 sink vertically a few feet." 



This pulsation of the earth's crust, if I may be allowed the expression, appears 

 to have been in periodical operation, and continued at intervals during the deposi- 

 tion of the Coal Measures. We accordingly find an alternation of many seams of 

 coal, sandstone, and shale, attaining in South Wales the extraordinary thickness 

 of 12,000 feet. In this field, which appears to be entirely of fresh water origin, 

 the number of coal seams is about 100, each accompanied by its under clay. That 

 the Coal fields are the remains of a vegetation which, after flourishing on the spot, 

 passed into the condition of a peat-moss, and then became submerged, is rendered 

 probable by the fact that the underclays contain the roots of stigmaria occupying 

 the original spots on which they grew. Stems of trees, still retaining their upright 

 position, are familiar to all miners, under the name of " coal pipes." 



"These coal pipes," again to quote Sir Charles Lyell, "are much dreaded by 

 miners, for almost every year in the Bristol, Newcastle, and other Coal fields, they 

 are the cause of fatal accidents. Each cylindrical cast of a tree, formed of solid 

 sandstone, and increasing gradually m size towards the base, and being without 

 branches, has its whole weight thrown downwards, and receives no support from 

 the coating of friable coal, which has replaced the bark. As soon, therefore, as 



