64 GEOLOGY OF THE LOTHIANS. 



ends only is visible, the mean breadth being about three feet 

 and a half ; it is vertical, and indurates the sandstone strata 

 which dip to the N. W. at 12°. At St George's mineral 

 well a vein of compact greenstone crosses the strata of sand- 

 stone and bituminous shale. In its progress through the 

 strata it entangles portions of the shale, which become com- 

 pletely indurated, and from the minute veins which shoot 

 from out the central mass into the stratified rocks, the high 

 state of fluidity in which the greenstone has been erupted is 

 apparent. (PI. VIII. Fig. 1 and 2.) On the north bank of 

 the river a thin stratum of clay-ironstone is shifted for about 

 a foot, and the vein of greenstone entangles a wedge-shaped 

 mass of bituminous shale. Like the other veins which we 

 have mentioned, this greenstone, as it approaches the strata, 

 passes into a yellowish-white claystone, of which the small 

 veins which arise from the chief mass are entirely composed, 

 — a fact at once shewing that the causes allowing the forma- 

 tion of the felspar have only existed in those portions of the 

 trap which were in contact with the traversed rock, or in 

 those which were of small size (PI. VIII. Sec. 3.) Above 

 the village of Bell's Mills another vein of greenstone is to be 

 found dipping with the strata to the N. by W. It is about 

 twelve feet in thickness, and approaches to the syenitic cha- 

 racter ; the slate which rests upon it is slightly indurated, 

 and when in contact with it the greenstone of the vein be- 

 comes compact. On the coast extending from Newhaven 

 to Queensferry, there is a fine section of the various rocks 

 of the coal-formation, and these, from their relations to ig- 

 neous masses, present several interesting appearances. 



About half a mile to the west of Newhaven there is a dis- 

 tinct example of the mantle-shaped mode of stratification ; 

 it is on a small scale, and a central point may be found, 

 from which the strata dip to all points of the compass. 



