246 ON A RECENT SUBSIDENCE AT MUCKING, ESSEX. 



Of course, in classifying variable sands, gravels and clays r 

 much depends on the nature of the information attainable by the 

 geologist recording sections in them. However, in the present 

 case the one important point is the depth to the Chalk from the 

 base of the London Clay, which is nearly the same at each 

 place. From the same volume of Mr. YYhitaker's memoir we 

 may learn that at Corringham a section showed that there were 

 Tertiary beds 137ft. in thickness between the London Clay and 

 the Chalk ; at Laindon 138ft., and at Vange 127ft. 6in. Thus,, 

 remembering that the uppermost 11 or 12ft. in the recent 

 Mucking subsidence are the lowest beds of the London Clay, and 

 that the older subsidences westward have some old Thames 

 gravel at the surface in addition, it is very improbable that the 

 Chalk is at a less depth than 150ft. beneath any of them. 



This depth makes it in the highest degree improbable that 

 these Mucking subsidences owe their existence to a natural 

 cause, such as the sudden filling in of a pipe in the Chalk. On 

 the other hand this thickness of the intervening beds also makes 

 it very improbable that they are the result of the collapse of 

 a denehole ending in the Chalk. And the vertical sides and great 

 breadth of the recent hole in themselves suggest the collapse of 

 a chamber or chambers at no great depth Then, while a 

 single pit of the denehole class might be a rare possibility (as in 

 the case of that at Eltham), yet it is in the highest degree 

 unlikely that a group of them would be made in a district where 

 the total depth would be from 160 to 170ft., that is, double the 

 depth attained by the deneholes of Hangman's Wood. At 

 Mucking, too, besides the mere depth, there would be water 

 difficulties, arising from the presence of clayey bands in the 

 Woolwich series, from which the Hangman's Wood pits 

 are free. 



In short, a single pit ending in the Chalk, where these 

 Mucking subsidences occur, might be a bare possibility, just as 

 a well of that or greater depth might be sunk for the supply o 

 some public institution, brewery or factory situated in a village. 

 But the existence of a group of pits of this depth and special 

 difficulty of construction is as unlikely as that of a group of very 

 deep wells for the supply of the cottagers in the village street. 

 In this district, too, where deneholes are known to abound 

 wherever the Chalk is at the surface, or not more than 60 feet 



