The Scottish Natiwalist, 53 



Lawers, and to a less extent on Ben Nevis, there can scarcely be said to 

 be a higher zone than the subalpine. On the former we have, indeed, 

 numerous plants belonging to the two highest zones, viz., alpine and supra- 

 alpine, crowded almost indiscriminately. The causes at work likely to have 

 produced such a congeries of plants on one and the same mountain have 

 often engaged the attention of West of Scotland botanists. Many theories 

 have been propounded, to be as often dismissed. One or two circumstances 

 have, however, rivetted my attention, and as they still cling to me in spite of 

 adverse opinions I think it right to state them fairly and candidly. 



** In the first place, no cryptogamic botanist who has repeatedly ascended 

 any of the more prominent of our western mountains can fail to be impressed 

 with the remarkable fact that there are special spots on each mountain, and 

 these generally ^^'ithin very restricted limits, where almost all the rarer 

 alpine plants (the word alpine being used in a general sense) may be seen 

 that are likely to be got in each individual case, and that, having once 

 alighted upon such spots, it is almost useless to investigate any 

 others. 



*' 2d. A little experience will further enable the botanist to satisfy himself 

 that such prolific spots are very generally in the form of ravines, or at least 

 hollows, including the sides of such ravines. 



** 3d. That such hollows have very generally a southern, or more strictly 

 a south-eastern exposure. 



** 4th. That these slope upwards in a north-western direction, and termi- 

 nate in a saddle-back, which is almost always of a lower elevation than the 

 rest of the general ridge bounding this hollow on the north. Such hollows 

 are well seen on Ben Lawers, Craig Chailleach, Ben Lomond, Ben Nevis, 

 &c. 



"5th. That the parts of the mountain on the other side of this saddle-back, 

 i.e., on its northern aspect, are singularly barren of such alpine rarities. 



'• Now taking Ben Lawers as our type, it can easily be ascertained by any 

 one even after a cursory survey that the nothem shoulder of the mountain, in- 

 cluding that of Craig-na-Gour, is worthless as a field of research ; indeed, I 

 cannot recall having ever detected there any moss of any consequence except 

 Dissodon splachnoides, and as this was found well up, near the head of the 

 so-called Corrie of Craig-na-Gour, which, in turn, is pi'otected on its north- 

 western aspect by high precipitous rocks, this spot cannot be reckoned as 

 forming an exception to the fact stated above. 



''6th. When it is stated, besides, that there are distinct evidences, in the 

 majority of cases, of glacial action high up on the sides of such ravines, but 

 few or none near their base, the conclusion to which the reader's attention 

 is called becomes evident, viz., that such hollows were protected dur- 

 ing the period of the glacial drift by solid masses of ice or glaciers, and 

 that such plants (or their spores) as flourished previous to this epoch were 

 not destroyed, but allowed to remain in statu quo. 



" Still referring to Ben Lawers, all the rare alpine mosses without 

 exception are found in the ravine, or on its lower slopes, which is situated 

 between the mountain and Craig-na-Gour on the west. It is notable also 

 that the truly alpine forms found in this ravine bear a close resemblance to 

 those corresponding to them from the Dovrefeldt Mountains in Norway, so- 



