1 4H y\ H CUNNINGHAM ON THE GEOGNOSY OF 



or two lines of cleavage to many slates. Impossible, how- 

 ever, though it may be, to explain the immediate actions 

 by which this change has been effected, still it appears in 

 some degree likely, that the presence of trap-rocks is con- 

 nected with this structure ; for here, as in every other 

 place where we have observed it, these are abundantly 

 developed. 



Limestone, which, after sandstone, is the most univer- 

 sally distributed stratified rock of Eigg, is of a compact 

 structure, of a bluish-grey colour, and has a conchoidal 

 fracture. It alternates with the sandstone, and contains 

 the usual belemnites, gryphytes, and ammonites of the 

 deposit ; but, on the great scale, exhibits nothing requiring 

 farther detail. The slate-clay, which is associated with 

 the sandstone and limestone, is soft, and of a grey colour, 

 and includes, in many places, numerous scales of mica. 

 None of the three rocks, however, which form the stratified 

 system of Eigg, severally hold any definite place in the se- 

 ries ; but, on the contrary, alternate regularly with each 

 other, constituting a deposit, the formation of the several 

 individuals of which has been strictly contemporaneous. * 



Having briefly noticed the stratified or Neptunian rocks 



* The stratified rocks which we have described as occurring in Eigg-, 

 are in many other of the Hebrides connected with strata which differ 

 from these, both in mineral and fossil characters. Little examination 

 is required to convince that they form only one series, and that to sub- 

 divide them into distinct groups, is, since nature has made no separa- 

 tion, a work of little utility. Though we could refer every stratum to 

 its analogue in any other country, say to those of England, nothing 

 would be gained, for as there the several members of the series, 

 though they have distinct names attached to them, belong to one great 

 geognostical group, and present only insignificant mineral and fossil 

 differences, so here the same is evident, and entitles us to consider that 

 there is no necessity to parcel out, into minute classes, the rocks of a 

 stratified deposit, which expresses, when its members are viewed col- 

 lectively, a system which had been formed uninterruptedly during a 

 well-marked epoch of the world's ancient history. 



