ULVA, &C. GENERAL DESCRIPTION. ,581 



ULVA,* GOMETRA, COLONSA, EORSA. 



WERE it not for the purpose of completing the mi- 

 neralogical map of the Western isles, it would scarcely 

 have been necessary to mention these, since both in 

 external aspect and structure, they are identical with 

 the neighbouring coast of Mull. 



Ulva and Gometra are separated from each other by 

 so narrow a sound, that from most points of view they 

 seem to constitute one island. The former is divided 

 from Mull at its eastern end by a shallow and narrow 

 arm of the sea, which increases to a wide bay where it 

 separates Gometra from the same island. The latter ap- 

 pears to ' attain an elevation of about 800 feet ; Ulva, 

 one of 1300 or 1400; both being composed of repeated 

 ranges of terraces rising in succession from the shore 

 to the summit. These present rocky faces of dark blueish 

 trap, either amorphous or marked by a columnar tendency. 

 On the shores, some low but very well formed ranges 

 of columns are to be seen; and in sundry places an 

 amygdaloidal mass is also visible, abounding in the two 

 varieties of zeolite most common on this coast, mesotype 

 and analcime, of which the latter is the most abundant. 

 There neither appears any general rule respecting the 

 relation between the amygdaloid masses and the solid 

 trap, nor are there any continuous beds of the former 

 substance. They are sometimes wanting altogether, at 

 others they are placed either above the trap or below it, 

 and in some cases they are interposed between two ranges 

 of columns. Although these ranges seldom exceed 

 twenty feet in height, they are very numerous, since 

 they skirt the whole south-western shore of both the 



* See the Map of Mull. 



