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DE. H. C. SOEBY ON THE APPLICATION OF [Maj^ 1 908, 



the Stoney- Middle ton specimens, of which I have ten excellent 

 microscopical sections of unusual size, it seems almost impossible 

 to explain why the pressure should have been at a maximum along 

 so complex and tooth-like a surface ; and sometimes I feel tempted 

 to conclude that a cause may have acted, about which we know 

 little or nothing. The quantity of carbonate of lime dissolved 

 and transferred to where the pressure was less must have been 

 considerable, as shown in the figure by the amount of shell 

 removed. 



It is chiefly in those Devonian limestones in which slaty cleavage 

 has been developed that surfaces of pressure-solution on a small 

 scale are common, and play an important part in modifying the 

 structure, since they have often conspired in altering the form of 

 joints of encrinites and other organisms. In a few cases, however, 

 notably in a specimen from Kingskerswel], the rock has been 

 greatly changed as a whole, and joints of encrinites altered from 

 about 1 : 1 to 1 : 4. There is also another interesting fact which 

 for a long time puzzled me — that is, the alteration in crystalline 

 calcite in which pressure has sometimes given rise to curved 

 cleavage, or broken up the crystal into thin layers of twinning, 

 similar to what can be produced by a knife, as shown by 

 H. Baumhauer.^ 



Oolites with Pressure-Solution. 



The most remarkable specimen in my possession is one from the 

 Carboniferous Limestone on the south side of the gorge at Clifton. 

 As will be seen from PI. XVIII, fig. 2, instead of the grains being 

 well separated or merely touching one another, as in Grantham 

 Oolite, they (as it were) interpenetrate to a considerable extent by 

 surfaces of pressure-solution, and yet their structure is not materially 

 disturbed. This interpenetration could not have occurred, if the 

 interspaces had been filled by infiltrated calcite before the rock 

 was subjected to great pressure. This seems to have acted in a 

 line perpendicular to the stratification, for there is little or no 

 interpenetration in the plane of bedding. In the part figured 

 the interspaces amount to only 11 per cent., which is a great 

 reduction from 26 per cent., and closely corresponds with the 

 change of dimensions calculated from the shape of the oolitic 

 grains, which is from 100 to 83. The production of this excep- 

 tional specimen may be explained by supposing that the interspaces 

 remained unfilled until after the rock had been exposed to great 

 pressure, and that the cavities were then filled by material possibly 

 transferred by pressure-solution from the altered oolitic grains. 



1 Zeitschrift fiir Krystallographie, vol. iii (1879) p. 588. 



