130 SEIL. GEOLOGY. 



predominant substances, and which will hereafter be 

 described at length in the account of the Craignish 

 islands, and in the general concluding remarks. To avoid 

 all ambiguity, I have preferred leaving it unnamed, to the 

 use of the term greenstone ; a name not very well applied 

 on many occasions, and often in danger of exciting an im- 

 proper association of ideas respecting geological relations. 



The rocks which accompany this and form the re- 

 mainder of the grey ridge, are a schistose and a compact 

 quartz rock, with micaceous schist, and more rarely, 

 chlorite schist ; all of these being members of the series 

 above mentioned, and therefore to be examined in preater 



' O 



detail hereafter, when their connexions will admit of a 

 more ample description. 



The next rock in the order of superposition, and conse- 

 quently, eastward, is the same clay slate that occurs in 

 the lowest position to the westward; and it here forms 

 the whole remaining portion of the island. As it differs 

 from the former in no respect, it requires no description ; 

 and I need only add that, like those beds, it is extensively 

 wrought for roofing slate. 



It is evident then that the clay slate alternates with 

 the other schistose rocks; an appearance very extensively 

 confirmed, not merely by the comparison of the positions 

 of the strata in different islands, but by their actual alter- 

 nations in many other places. However much this obser- 

 vation may differ from those of others respecting the 

 natural affinities of clay slate, it can only be said that it is 

 a faithful record of the appearances. 



The last of the stratified rocks to be seen in Seil, occurs 

 but in small quantity, and is found on the north-western 

 side of the island. It is a portion of the secondary strata 

 already described in Kerrera and Inish Capel, but is 

 neither extensive nor remarkable enough to require a 

 more detailed record. Its existence suffices to establish 

 the general continuity of character among these three 

 islands, no less thsrn tlu- respective resemblance of the 



