834 COAL 



a visit made to the island in I860 Professor Ramsay and Mr. H. W. Bristow observed 

 certain beds of a coal on the west side of the island, in Alum Bay. 



These coal-seams at Alum Bay are found in the Bracklesham beds of the Middle 

 Bagshot series, appertaining therefore to the Middle Eocene Tertiaries. The formation 

 reappears at the opposite extremity of the Isle of Wight, namely, at Whitecliff Bay 

 near Undercliff) the spot already mentioned. But the existence of the coal-seams at 

 the latter spot was not detected by the Geological Survey until very lately, -when the 

 scams in question -were observed by Mr. Penning, in company with a miner from the 

 Forest of Dean, named Richard Gibbs. The seams were apparently of greater 

 width than those at Alum Bay, although a thickness of seven feet could not be made 

 out unless it were by adding several contiguous seams together. The discovery was 

 communicated to Mr. Bristow, who thus describes them : 



' The strata comprised between the well-known glasshouse sands at the biisc of 

 Headon Ball and the pipe-clay-bearing sands and clays overlying the London Clay, 

 and grouped together by Mr. Joshua Trimmer as the Middle Bagshot series, were sub- 

 divided by him into Barton Clay and Bracklesham Beds. 



' The latter are represented in Alum Bay by clays and marls in the lower part, and 

 by white, yellow, and crimson sands above. The lower beds are remarkable for the 

 quantity of vegetable matter contained in them, not, however, in the shape of leaves, 

 as is the case in some of the Lower Bagshot Beds, but in the form of lignite, constitut- 

 ing solid beds from fifteen inches to two feet three inches thick. Four of these beds, 

 when fully displaced, constitute conspicuous objects in the cliff, where they project out 

 of the softer strata, and on the shore, from their black and coal-like appearance. 



' These beds of coal were recently more than usually well displayed in consequence 

 of the prevalence of long-continued wet weather having worn away the soft interven- 

 ing strata in which they are imbedded. On examining them during a brief visit 

 made to the Island, in company with Professor Ramsay, during the autumn of 1860, 

 it appeared evident that the beds in question occur more in the manner of ordinary 

 coal than of mere lignite. Like true coal, each bed was based upon a stratum of clay, 

 containing, apparently, the rootlets of plants, as in the underclay of the true coal- 

 measures. The underclays, which occur beneath each bed of coal of carboniferous date, 

 having been the soil which supported the vegetation which, by certain chemical 

 changes, became subsequently mineralised and converted into coal, it is reasonable to 

 infer from the presence of similar underclays beneath the coal in the Bracklesham 

 Beds at Alum Bay, that the plants out of which it was formed grew on the spot, and 

 were not drifted from elsewhere and deposited afterwards in the places where they 

 are now found, as was undoubtedly the case with regard to the vegetable remains 

 contained in the pipe-clay beds of the Lower Bagshot series.' 



The following section of the Bracklesham beds in Alum Bay, as given by 

 Mr. Bristow, in his ' Memoir on the Geology of the Isle of Wight,' will show the true 

 position occupied by those lignite beds in the series (in ascending order) : 



Dark chocolate-coloured marls and carbonaceous clay, with much ft. in. 



Lignite and Gypsum 39 6 



ft. in. 

 Clays and marls . . . . . . . 15 3 



Lignite band . . . , .. . .16 



Clays and marls 33 



Lignite band 13 



Clays and marls .60 



Lignite band . " v- ., 23 



Clays and marls 43 



Lignite band 9 in. to 1 



Clays and marls , 50 



39 6 



Whitish marl clay . . 25 



Sands (principally white), light tawny yellow in the upper part ; the 



lower three feet crimson . . . . . . . .46-0 



Conglomerate of rounded flint pebbles cemented by oxide of iron 1 ft. to 1 6 



Total Ill 



The pebbles are of various sizes, the largest a foot in diameter. 



The Lignite of Bovey already referred to, may be regarded as of a similar character 

 to this of the Isle of Wight, notwithstanding the differences which have been pointed 

 out, and the coal of Brora is not very dissimilar in its general character. 



The coal of the Woalden strata is generally termed ' lignite,' though some ap- 

 proaches very closely to the character of a true coal. Whether we call it lignite or 



