836 MisceUaneous — The Blachheath Subsidences. 



The way some reasoners have of dealing with land and water 

 reminds me of nothing so much as the instructions given to an Irish 

 labourer, who asked his master how he was to dispose of a certain 

 lumj) of rubbish. He was told " to dig a hole to put it in." 

 " But," says he, " What am I to do with the stuff out of the hole? " 

 The answer was pat : " Dig a hole big enough to hold both." 



T. Mellard Ekade. 



REPLY BY THE EEV. H. G. DAY TO THE EEV. 0. FISHER. 



Sir, — Mr. Fisher cavils at my proof (Geol. Mag. p. 237). I 

 must apologize for the accidental interchange therein of the symbols 

 OL and /3 ; a slip which affects neither its validity nor its relevance. 



Mr. F. claims that I should correct his similar lapsus. Had this 

 been my province, I should certainly have commenced by asking 

 him to explain under what circumstances he finds it impossible to 

 pass a vertical plane through the major axis of his ellipse (p. 21, 

 line 2). Mathematicians had been accustomed to believe that any 

 line could lie in a vertical plane. H. G. Day. 



Dvnisc;:EXiij.^D^EOTJS. 



The Blackheath Subsidences. — Attention has been called in 

 Nature (Feb. 17, 1881), and in The Engineer (Feb. 4, and March ]8, 

 1881) to a series of subsidences that have taken place at Blackheath. 

 In April, 1878, a subsidence of the ground occurred near a place 

 called Eotten Row, the hole being 8 or 9 yards in circumference ; 

 in November, 1880, two holes appeared, one not far fi'om the gravel- 

 pit below Eliot Place and Heath House, and the other nearer to 

 All Saints' Church. 



The district is occupied by the Lower London Tertiaries — the 

 Chalk occurring at about 100 feet from the surface ; and several 

 natural causes have been suggested to account for the production of 

 these holes. 



In seeking for an explanation, Mr. T. V. Holmes (Engineer, 

 March 18) recalls attention to the discovery in 1878 of a pit, in all 

 probability a Danes' Hole, at Eltham Park, within three miles of 

 Blackheath, and mentions other ancient artificial excavations or 

 "Danes' Holes" about Bexle\', Chiselhurst, and in "Jack Cade's 

 Cave " at Blackheath itself. He considers that the popular tradition 

 that these Holes were originally intended as places of security for 

 persons and property from Danish and other pirates and robbers, 

 seems to be the most reasonable explanation of their existence. 



Nevertheless, the question of their origin ought not to remain in 

 abeyance, and it may be mentioned that a committee, comprising 

 members of the Lewisham and Blackheath Scientific Association 

 and of the West Kent Natural History Society, has been formed for 

 the purp)ose of investigating the matter, and they invite contributions 

 towards their object. 



In connexion with this subject attention may be re-directed to a 

 letter from Mr. H. Norton, F.G.S., on the Pits of the Haute Marne, 

 see Geological Magazine for June, 1877, Decade II. Vol. IV. p. 286. 



