500 S. W. Bristow and S. B- Woodward — 



mud, with the organisms living in, and common to, a great river. 

 In the latter case the vegetable growth is covered up by marine silt, 

 sea-shells, etc. 



One difficulty, however, not met by these illustrations, and re- 

 quiring to be explained in order to clear up the origin of coal, is its 

 exceeding purity and freedom from admixture of foreign matter ; each 

 coal-seam being, so to say, completed and then sealed up, so that its 

 hydro-carbons should all be retained in the best possible condition 

 for fuel. This could not have taken place in a mere Cypress-swamp 

 or Mangrove-swamp, such as one sees in tropical America at the 

 present day. 



If, however, you picture a vast alluvial plain covered with a 

 Cryptogamic forest of giant Lepidodendra and Sigillaria growing on 

 a stiff tenacious clay-soil, capable of retaining the rain-fall, then you 

 have the conditions suited for the rapid accumulation of peat, and 

 that is the purest form we know of any great accumulation of 

 vegetable matter unmixed with foreign material, which is the 

 peculiar feature of the Coal-measures. 



If any stronger argument than we have used against claiming for 

 the Coal-period special and abnormal conditions were needed, it is 

 to be found in the fact that we have Coal of Tertiary and Secondary 

 ages as well as Primary or Paleozoic. 



The Tertiary Brown Coal of Germany and Eussia, the Bovey- 

 Tracey Lignites, the Miocene Coal of the Mackenzie Kiver, North 

 America ; the Kimmeridge Coal ; the Brora Coal (Oolitic in age) ; 

 and, indeed, judging by the plant-remains, there is good reason for 

 believing the Coal of China to be of Secondary age ; the accumulated 

 growth of plants, such as Cycads, Taxinese, Araucarians, Equisetacese 

 and Ferns, corresponding in character with those found in the 

 Oolitic plant-beds near Scarborough, Yorkshire. 



Again, there is reason to believe that some coal may be of Devonian 

 age, for Dr. Dawson has already made known a land- flora and fauna 

 of Devonian times, agreeing somewhat with the plants which form 

 the true coal. 



Lastly, Lycopodiaceous seeds occur in the Upper Silurian, and 

 lower still, we get Graphites, which may owe their origin (as the oil- 

 bearing strata of pre-Carboniferous age no doubt did) to the de- 

 structive distillation of old Silurian Coal-beds, the products of old 

 land-surfaces, distilled in Nature's own retort.^ 



II. — Eemauks on the Pkospects of coal to the South of the 



Mendips. 



By H. W. Bristow, F.R.S., F.G.S., and H. B. Woodward, FG.S., of, the 

 Geological Survey of England. 



THE question as to the probable existence of a Coal-field on the 

 south side of the Mendips having lately been j^rominently 

 brought before the public in the Eeport of the Eoyal Coal Com- 



1 Eeadalso before the British Association, Edinburgh, Section C, August, 1871. 



k 



