154 Geological Society : — 



fusion as the slags of our furnaces or the erupted lavas. When the 

 constituent minerals of solid granite, far from contact with the stra- 

 tified rocks, are examined, it is seen that they also contain fluid- 

 cavities. This is especially the case with the quartz of coarse- 

 grained, highly quartzose granites, in which there are so many, that 

 the proportion of a thousand millions in a cubic inch is not at all un- 

 usual ; and the enclosed water constitutes from one to two per cent, 

 of the volume of the quartz. However, besides these fluid-cavities, 

 the felspar and quartz contain excellent stone-cavities, precisely ana- 

 logous to those in the crystals of slag, or erupted lavas ; and thus 

 the characteristic structure of granite is seen to be the same as that 

 of those minerals formed underaqueo-igneous conditions in the blocks 

 which are ejected from modern volcanos; and the very common 

 occiurence of minute crystals inside the fluid-cavities still further 

 strengthens this analogy. 



The conclusion to which these facts appear to lead, is that granite 

 is not a simple igneous rock, like a furnace- slag, or erupted lava, but 

 is rather an aqueo-igneous rock, produced by the combined influence 

 of liquid water and igneous fusion, under similar physical conditions 

 to those existing far below the surface at the base of modern volcanos. 



These deductions of the author, therefore, strongly confirm the 

 views of Scrope, Scheerer, and EKe de Beaumont ; and he agrees 

 with them in considering it probable that the presence of the water 

 during the consolidation of the granite was an instrumental, if not the 

 actual cause of the difference between granite and erupted trachytic 

 rocks. 



December 16, 1857.— L. Horner, Esq., V.P.G.S., in the Chair. 



The following communications were read : — 



" On the Boiing through the Chalk at Harwich." By Joseph 

 Prestwich, Esq., F.R.S.,F.G.S. 



In this boring, which is made near the Pier at Harwich, the fol- 

 lowing succession of strata has been met with : — Earth, 10 ft. ; Red 

 Gravel, loft.; London Clay, 23ft.; Coarse dark Gravel, 10ft.; 

 Plastic Clay, 7 ft. ; Bluish Clay with Greensand, 3^ ft. ; Green and 

 Red Sand intermixed, 5 ft. ; Blue Clay, 3 ft. ; Chalk with flints, 

 690 ft. ; Chalk without flints, 160 ft.; Rocky Chalk in thin layers, 

 38 ft. ; Greensand and Gault, 22 ft, ; Gault with sand, 39 ft. ; Dark 

 Grey Slaty Rock, 44^ ft. Total 1070 feet. From this section it is 

 evident that the Tertiaries, Chalk, Upper Greensand, and the Gault 

 were met with in the usual order, though the last had less than the 

 usual thickness ; and that at a depth of 1025 feet an anomalous clay- 

 slate occurred. This rock is without fossils, and is intersected with 

 lines of joints or cleavage and of bedding, at considerable angles to 

 the vertical axis of the bore-hole. This result of the boring at Har- 

 wich has necessarily an important bearing on the evidence furnished 

 by the Kentish Town Well (Quart. Journ. Geol, Soc. vol. xii. p. 6) ; 

 and, combined with the fact of coal-rocks having been found by the 

 deep boring at Calais, tends to prove Mr. Godwin-Austen's view of the 

 existence of a westward extension of a ridge of the crystalline and 



