

GARVELOCH ISLES. GEOLOGY. 159 



worthy of notice. As the same substances, in the same 

 order of position, are found in all these islands, the same 

 description will serve equally for the whole. The greater 

 or less proportion between one species of stratum and 

 another, which may be observed in the different indi- 

 viduals, depends solely on their several positions ; or on 

 that of their parts eastward or westward of a given line 

 which may be considered as dividing the one set of strata 

 from the other. Thus, in one, the limestone will be found 

 to exceed ; while in another it falls short in quantity when 

 compared with the schistose rocks ; or is even absent 

 altogether. 



* Commencing the examination of these rocks from the 

 eastern side, as the uppermost in position, a series of beds 

 is found, consisting principally of a schistose conglome- 

 rate ; which will be seen hereafter to occur in Isla, and 

 which I have also observed in Schihallien; interposed 

 there, as it is here, among the strata of quartz rock, mica- 

 ceous schist, and limestone, which constitute the chief part 

 of that mountain. Its basis is a schist varying in aspect 

 and character between a quartzose micaceous schist and 

 an argillaceous one ; or, if we were merely to consider 

 the definition, resembling more nearly graywacke. Occa- 

 sionally it passes into a pure quartz rock, and distinct 

 beds of that substance, free from any of the foreign sub- 

 stances which characterize the prevailing beds, occur in 

 alternation with it. Distinct beds of argillaceous schist 

 are also found interstratined with this conglomerate 

 schist; appearing to prevail chiefly at the lower parts 

 where it first begins to pass into the accompanying lime- 

 stone. The imbedded substances which produce the con- 

 glomerate structure, are, granular limestone of a yellowish 

 and reddish white colour, red or white quartz, and. gra- 

 nite. The fragments vary much in size, from that of 

 a pea to a foot or more in diameter, and they are almost 



* Plate XV. fig. 4. 



