504 Dr. Mac Culloch on Stafa. 



upwards, and generally exhibit specimens of radiated mesotype and 

 of analcime. The cubical zeolites (chabasite) are of rare occurrence, 

 and the mesotype is seldom granular, and never, as far as I saw, 

 capillary. The lamellar variety of stilbite, is occasionally found filling 

 the intervals of approximate columns. I did not observe any zeo- 

 lites in the larger and more perfect columns, but in the smaller and 

 more irregular ones they occur, though rarely. 



If we were to view the island only from the southwestern side, 

 and at half tide, we should conclude that it has been formed of 

 three distinct deposits, or beds of basalt. Of these the lowermost 

 appears in some places amorphous, but it is not easy to see enough 

 of it to judge whether it actually forms a continuous bed. It is 

 only from the analogy of Canna, and the other basaltic islands of 

 this sea, that we should be tempted to generalize this conclusion. 



The next bed, is that which is divided into those large columns 

 which form the most conspicuous feature of Staffa, and it varies 

 from SO to 50 feet in thickness. I'he upper one appears at a 

 distance to be an uniform mass of amorphous basalt, but on a 

 nearer inspection it is found to consist of small columns, laid and 

 entangled in every possible direction, often horizontal, and generally 

 curved. It is this bed which forms the ponderous cap (as it is 

 called) which crowns the summit of the gvdind facade. 



Although the great columnar bed occupies but a small portion of 

 the whole exterior face of the island, the columnar form is perhaps 

 predominant throughout the whole. Yet it would be equally 

 difficult, as useless, to attempt to determine its proportion to the 

 amorphous part where they are irregularly mixed, as they are at 

 the northern and eastern sides. On these sides also the division 

 into distinct beds such as I have described above, is by no means 

 easy to trace, and possibly it does not exist. 



