136 Analyses of Books. [August, 



mens of this substance. But wherever it approaches or comes 

 in contact with the granite, it becomes highly indurated, effer- 

 vesces slowly with acids, and gives on analysis a large propor- 

 tion of siliceous matter. All the varieties of this marble contain 

 more or less of mica, which excludes it from the statuary's use, 

 though it is perfectly applicable to various architectural and 

 ornamental purposes to which its greyish hue and low tone of 

 colour are more applicable than the dazzling white of the 

 Carrara marble. Steatite and noble serpentine are found mixed 

 with and imbedded in this marble, as also is the case with trerno- 

 lite, which latter mineral besides constitutes thin beds alternat- 

 ing with the marble. Beds of sahhte, affording several varieties 

 of this substance, are likewise associated with the limestone. 



From the above and other similar appearances, Dr. M. 

 concludes the general structure of this part of the country to be 

 composed of regular, even, and defined alternations of quartz 

 rock, schist, and limestone, resting on granite, the immediate 

 . covering of the granite being sometimes one, sometimes another 

 of the superincumbent stratified beds. In eveiy instance where 

 the granite is actually visible in contact with the neighbouring 

 rocks, great confusion and disturbance are apparent, consisting 

 in a general mixture of all the stratified rocks with the granite, 

 and a total discomposure of their regularity, being at the same 

 time accompanied by the passage of minute veins from the mass 

 ,of granite into the stratified rocks. Where on the contrary the 

 beds lie out of the immediate vicinity of the granite, they retain 

 their parallelism and regularity, its influence appearing to extend 

 to a very short distance beyond the point of actual contact. 



III. — 9. Sketch of the Geology of the south-weslern Part of 

 Somersetshire. By L. Horner, Esq. F.R.S. 



The high part of the district here described, including the 

 Quantock hills, is elevated from 800 to 1,600 feet above the 

 level of the sea, and is occupied, generally speaking, by a grey- 

 wacke formation, consisting of sandstones, more or less clayey 

 and fissile, of schist, coarse or fine slaty, and often inclosing 

 thick irregular beds of limestone, abounding for the most part 

 in madrepores. Curvatures, contortions, and fractures, are of 

 frequent occurrence in the various beds of this formation, indicat- 

 ing it to have been subjected to the violent impulse of some 

 unknown agent, while the beds still preserved a greater or less 

 degree of plasticity. 



The rock on which this greywacke rests is unknown ; in a 

 single instance Mr. H. discovered a vein of granite traversing 

 the slate, and as usual producing a degree of induration on 

 those parts of the rock which are actually or nearly in contact 

 with it. 



The greywacke is bounded in every direction by that deposit, 

 called by the name of red rock, red marl, red ground, Sec. which 



