Mr. Clough has given me the details of an interesting case of this kind observed by him in Glen Tarsan, Eastern Argyleshire:--"For an inch or so from the edge of this dyke," he remarks, "porphyritic felspars giving squarish sections, and ranging up to one-third of an inch in length, are so abundant as nearly to equal in bulk the surrounding groundmass. For the next inch and a half, they are decidedly fewer, occupying perhaps hardly an eighth of the area exposed. Then for a breadth of three inches they come in again nearly as abundantly as at the sides; after which they diminish through a band 27 inches broad, where they may form from 1/8 to 1/12 of the rock." He found another case where, in a dyke several yards wide, porphyritic felspars, sometimes an inch long, are common along the eastern margin of the dyke in a band about two inches broad, but nearly absent from the rest of the rock. Elsewhere the crystals are grouped rather in patches than in bands. Among the dykes south of Oban some similar instances of coarsely porphyritic felspars may be observed. Not only are these porphyritic felspars apt to occur in bands parallel with the outer margins of the dykes, but they tend to range themselves with their longer axis in the same direction, thus even on a large scale, visible at some distance, showing the flow-structure, which is so often erroneously regarded as essentially a microscopic arrangement, and as specially characteristic of superficial lava-streams. Mr. Harker in his survey of Strath, Skye, has met with some remarkable examples of the enclosure and incorporation of foreign materials in the younger group of dykes which in that district traverse the granophyres and gabbros. He remarks that the great majority of these dykes are basic, and he has found them to be capable of convenient division into two groups. 1st, Non-porphyritic basic dykes with a specific gravity between 2·87 and 2·97, and an amygdaloidal structure affording clear indication of flowing movement, either at the sides or along a central band. These dykes do not greatly differ from those of pre-granophyre eruption. 2nd, Porphyritic basic dykes which present features of peculiar interest. The porphyritic (or pseudo-porphyritic) elements, according to Mr. Harker's observations, are constantly felspar, frequently subordinate augite, and exceptionally quartz. The felspars have for the most part rounded outlines with a bordering zone of glass cavities apparently of secondary origin. The augite, in rounded composite crystal-grains, differs from that of the groundmass and resembles the augite of the gabbros. The quartz-grains are likewise rounded, and show sometimes a distinct corroded border.