150 MR CUNNINGHAM ON THE GEOGNOSY OF 



examples of these may be observed near Laig : they do 

 hot, however, require any particular notice. The effects 

 which trap -rocks produce on the strata are here never very 

 conspicuous ; where junctions are, however, to be observed, 

 they exhibit the usual appearances in a more or less marked 

 manner, the sandstone becomes quartzose, and the lime- 

 stone crystalline. Near the Bay of Laig the latter has a 

 fibrous structure, which, from our only noticing it in that 

 part of the stratum in contact with a trap-vein, is, in all 

 probability, to be considered as having been produced by it. 

 The fibres of this limestone never exceed more than three 

 inches in length, are at right angles to the strata, and are 

 separated from the compact limestone by a well-defined 

 line. This appearance is difficult to explain, inasmuch as 

 the changed rock might be expected to pass gradually into 

 that which is unaltered. The absence of a transition of 

 what, in accordance with Plutonic doctrines, are considered 

 altered rocks into those which can only be viewed as un- 

 altered, is, in many localities in Scotland, in no small de- 

 gree remarkable ; and the fact that they occasionally alter- 

 nate is a phenomenon which is inexplicable in the existing 

 state of our knowledge of the laws which regulate subter- 

 raneous actions. Near the Ru Stoir Scalleadh, which forms 

 the most northern part of the island, there are several ex- 

 amples of envelopment, masses of the shale being com- 

 pletely included in the trap, and converted into flinty 

 slate ; the usual fossils are present, and may be traced from 

 an incipient to an almost perfect obliteration. The indu- 

 rated shale of Eigg, as that of other points in Scotland, ac- 

 quires a dull aspect after a fresh fracture is exposed to the 

 air for a length of time. 



The trap of Eigg occurs under the various forms of 

 greenstone, basalt, amygdaloid, and tuffa. In structure, 



