EGG. GEOLOGY. 515 



this rude colonnade being in different places wrought 

 into caves of moderate dimensions. Among the columnar 

 beds are interposed amorphous basalt and amygdaloids 

 containing nodules of calcareous spar, chalcedony, and 

 zeolites; the whole alternating in the usual irregular 

 manner. In some places there are also to be seen small 

 beds of siliceous schist, and of iron clay, substances veiy 

 frequently found among the stratified trap rocks of the 

 Western isles. 



It was observed at the beginning of this description 

 that there was a general parallelism and evenness of posi- 

 tion to be traced throughout the whole of this mass of 

 beds. It is in fact very remarkable, and is particularly 

 worthy of notice, as it rarely happens but that some dis- 

 turbance, fracture, or bending of the stratified rocks 

 occurs where they are in contact with trap. In this place 

 the thinnest as well as the thickest of the trap beds are 

 equally parallel to the sandstone and to the calcareous 

 strata among which they lie; those irregularities alone 

 being excepted which proceed from the occasional exte- 

 nuation and consequent disappearance of one or other of 

 these associated strata. In the account of Sky I have 

 described similar circumstances as existing among the 

 beds of lias on the eastern shore of Trotternish, although 

 the alternations there take place among masses of greater 

 dimensions ; and it was also proved that in every case of 

 this nature there occurring, an interference is somewhere 

 to be discovered even after a mile in length of regular pa- 

 rallelism had been preserved. That I did not discover such 

 interferences in the present instance is no proof of their 

 non-existence ; yet, admitting that they do exist, there may 

 still appear some difficulty in explaining the nature and 

 causes of the appearances in question. This difficulty con- 

 sists in the evenness preserved among alternations so nume- 

 rous and strata so thin. Yet as the stratified rocks are here 

 in no instance prolonged for any great space without some 

 interruption and change of composition and proportions, 



