Tol. 52.] THE TERTIAEY BASALT-PLATEAUX OF N.W. EUROPE. 375 



wall 500 feet high. Though I could not certainly trace any single 

 column continuously from bottom to top of the precipice, many of 

 them must be at least 300 or 400 feet long. No other sill in the 

 British Islands forms such a noble escarpment as this. 



In contrast to such enormous thicknesses of intrusive material, 

 instances may be culled from the same belt of sills where the molten 

 rock has been injected in thin cakes and mere threads into the 

 Jurassic sandstones and shales, or into the shales and coals inter- 

 calated among the plateau-basalts. Thus, on the cliff immediately 

 north of Ach na Hannait, between Loch Sligachan and Portree 

 Bay, the section which is represented in fig. 21 may be seen. 



Fig. 21. — Section of thin intrusive sheets and veins in carbonaceous 

 shales lying among the plateau-basalts. Cliff north of Ach na 

 Hannait, between Portree Bay and Loch Sligachan. 



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At the base lies a vesicular dolerite with a slaggy upper surface (a). 

 Next comes a zone of sedimentary material about 5 or 6 feet 

 thick, -the lower portion consisting of an impure coal, which passes 

 towards the right hand into brown and grey carbonaceous shale 

 -with plant- remains (6). This coaly layer has been already alluded 

 to as probably lying on the same horizon with the coal of Portree. 

 Traced northward, it is found to have a bed of fine tuff beneath it, 

 and sometimes a volcanic breccia or conglomerate. It fills up rents 

 in the underlying slaggy lava, and was undoubtedly deposited upon 

 the cooled surface of that rock. Immediately above this lower band 

 the black carbonaceous shale (d) which follows has been invaded by 

 an extraordinary number of thin cakes or sills, and also by veins 

 or threads of basalt. For a thickness of 2 or 3 feet the band 

 consists mainly of these intrusions, which, in the form of a fine 



