HAPDWICXE'S SCIENCE-GOSSIP. 



manor, gives a strong presumption that no such 

 attempts have, ever been made. The "other 

 commons " alluded to by Mackenzie may well have 

 been the; others on the Blackheath-Erith plateau, 

 of which those of Woolwich and Plumstead are the 

 nearest to Blackheath. 



The supposed interference of the Government to 

 check coal-mining is a tradition, doubtless, of many 

 districts. I remember meeting with it in Cumber- 

 land three or four miles S.W. of Carlisle, when 

 endeavouring to trace the boundaries of the Lias 

 outlier there, the district being entirely covered by 

 a considerable thickness of Glacial Drift. A farmer 

 of whom I made enquiries as to wells, etc., told me 

 that he had heard of the discovery of coal at a spot 

 close by his farm, but that it was said that mining 



But at Blackheath and the district around it there 

 can never have been any mystery as to the general 

 geological structure, such as may exist where the 

 older rocks are uniformly covered by a considerable 

 thickness of Glacial Drift, and the surface features 

 throw no light upon the arrangement of the under- 

 lying rocks. Few districts, indeed, have a more 

 obvious general structure than that of Blackheath. 

 The plateau, of which Blackheath forms the western 

 end, extends along the course of the Thames from 

 Greenwich to Erith, a variable breadth of alluvium 

 or river gravel lying between its northern edge and 

 the river. On its northern edge sections, here and 

 there, show Chalk at its foot, covered by Thanet 

 sand and the sands and clays of the Woolwich series, 

 the surface being composed of the Blackheath pebble 





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RG foyer GtclvcL .A A« T T^^tStvruL B. R Blffikhtalli. 



^ The. FcuisW* ejraj:th.oSL,tu}Tvcs do uX>lfoL,l>, 

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had been stopped there by the interference of Govern- 

 ment. This patch of Lias consists mainly of dark 

 shales with thin bands of limestone, and, apart from 

 its fossil contents, would naturally be supposed to be 

 Coal-measures coming up from beneath the red 

 Triassic rocks around it rather than Lias (a formation 

 not elsewhere known in the district) resting upon 

 the Triassic beds ; for there are plenty of Carboni- 

 ferous rocks on all sides beyond the red beds. The 

 Lias outlier appears to have been bored for coal at 

 various times during the last 250 years, one boring 

 in 1781, having penetrated through it to the Tri- 

 assic rocks beneath. And the popular view as to 

 the affinities of its dark shales is attested by the 

 name "Coalfeli Hill," applied to a slight eminence 

 within its borders about two miles west of Carlisle. 



beds, except where these last-named strata are them- 

 selves covered by London clay, as at Shooters Hill. 

 It is indeed the immense improbability that a skilled 

 miner of any period could ever have been deceived 

 into thinking coal attainable beneath Blackheath 

 which makes the existence of the popular tradition so 

 remarkable, and so worthy of an attempt to explain it. 

 In the Woolwich beds which underlie the Black- 

 heath pebble beds, thin bands of lignite sometimes 

 occur, one being now visible at Loampit Hill, 

 Lewisham (about a mile from Blackheath), from 

 three inches to six inches thick. But as the forty 

 feet of pebble beds at Blackheath are represented 

 at Loampit Hill by a pebble band of a few inches 

 only, the natural inference would be that the Black- 

 heath plateau was one of the least likely places any- 



