THE TRAP ISLANDS. 69 



the peninsula consists of a mass of trap, the general extent 

 of which (on the shore only) is indicated, for the sake 

 of this comparison, in the map of Mull. Between the 

 trap and the gneiss is found a body of strata, consisting 

 of limestone followed by sandstone, where the series is 

 complete : in other cases, only one of these rocks is pre- 

 sent. In a few situations coal also occurs. 



The limestone corresponds in every respect to that 

 which is found near Achnacrosh : being of the same com- 

 position, and containing the same organic remains. The 

 sandstone also, and the accompanying coal, are similar 

 to those found at Carsaig. 



With respect to the position of these strata, they are 

 necessarily regulated by the inclinations of the surface 

 of gneiss on which they are deposited, and they present, 

 in consequence, every variety of dip. Their peculiar situa- 

 tion also, causes the same apparent disjunction that is so 

 remarkable in Mull; since they can only be traced in 

 those places where the common boundary of the trap and 

 the gneiss is exposed to view. This circumstance however, 

 appears here under a form highly interesting, and illus- 

 trative of the real structure of that island. Wherever 

 this conterminous line is visible, the strata are tfound 

 lying between those two rocks, even where the trap occu- 

 pies insulated portions on the surface of the gneiss. From 

 this it may be concluded that the deposit of the secondary 

 strata is complete, beneath the trap ; at least within certain 

 exceptions of interference, or of partial removal, on which 

 it is now unnecessary to dilate. 



To transfer this reasoning to Mull, it appears that 

 although these strata cannot there be traced with even 

 the same limited regularity, detached parts of the series 

 are found scattered throughout the island. It has been 

 shown, that limestone containing gryphites, ammonites, 

 and belemnites, is found near Achnacrosh. There is a 

 perfect identity between this rock and the corresponding 

 limestone on the opposite shore of Morven ; and although 



