﻿Vol. 64.] QUANTITATIVE METHODS TO THE STUDY OF EOCKS. 225 



only the carbonate of lime that has been removed by solution, and 

 the whole of the insoluble material of the stone has been left, as 

 carefully determined by suitable means. 



An equally striking example of pressure-solution was described 

 in my address to the Geological Society/ in which I showed that 

 in a Devonian limestone at Ilfracombe the joints of encrinites have 

 been partly dissolved where the pressure which produced the 

 cleavage was at a maximum, and the dissolved calcite has crystal- 

 lized out where the pressure was at a minimum. Until quite 

 recently I did not recognize fully how important a part this action 

 plays in many other cases. 



What I propose to call surfaces of pressure-solution are 

 often numerous and small ; but some years ago I obtained from the 

 Carboniferous Limestone of Stoney Middleton (Derbyshire) speci- 

 mens in which they are unusually large. The normal characters 

 are layers of dark, apparently bituminous, material extending over 

 a considerable area, passing up and down like larger and smaller 

 interlocking teeth. Sometimes one of these layers branches into 

 two, which may again unite, and they cannot have been due to 

 stratification. The most probable origin of the bitumen is that 

 it is a residue of the solution of the limestone ; and that solution 

 of carbonate of lime has occurred is clearly proved, by the manner 

 in which the layers pass into the shells of brachiopoda and into 

 encrinites. This is shown by the accompanying text-figure. In 



the centre, not sha- 



Tooth-liJce structure penetrating, hy removal, ded, is a portion of 



a fossil shell and the surrounding lime- a shell with well- 



stone, most probably by pressure-solution, preserved structure, 



(^Mag7iified J/, diameters,) and, as will be seen, 



the zigzag bitu - 

 > - i minous layer (shown 



\. \ black) passes quite 



l#^* 0%%^^ ^ through the centre, 



^'' \ and partly on each 



, , \ side into two de- 



4 pressions nlled with 

 the limestone (shown 

 I I 'J \ shaded throughout). 



j ,- ij \ The laminar struc- 



i ^ ; **^ ; ture of the shell 



\ ^ I seems to have slightly 



' I influenced the di- 



_. „„ .. , . J rection of solution. 



Taking all the facts 

 into consideration, it seems as though both pressure and solution 

 have acted, and in some cases their combination will explain 

 the facts. However, when we come to examine the detail of 



' Quart. Journ. Geol. Soc. vol. xxxy (1879) Proc. p. 89. 



q2 



