RAMBLES OF A GEOLOGIST. 317 



one thousand two hundred to one thousand five hundred feet 

 over the sea-level ; the common bracken (Pteris aquilina) at 

 about the same height ; and corn is never successfully culti- 

 vated at a greater altitude. Where the hazel and bracken 

 cease to grow, it is in vain to attempt growing corn.* In 

 the period of the boulder-clay, then, when the existing shells 

 of our coasts lived in those inland sounds and friths of the 

 country that now exist as broad plains or fertile valleys, the 

 sub-aerial superficies of Scotland was restricted to what are now 

 its barren and mossy regions, and formed, instead of one con- 

 tinuous land, merely three detached groupes of islands, the 

 small Cheviot and Hartfell group, the greatly larger Gram- 

 pian and Ben Nevis group, and a group intermediate in size, 

 extending from Mealfourvonny, on the northern shores of 

 Loch Ness, to the Maiden Paps of Caithness. 



The more ancient boulder-clays of Scotland seem to have 

 been formed when the land was undergoing a slow process of 

 subsidence, or, as I should perhaps rather say, when a very 

 considerable area of the earth's surface, including the sea-bot- 

 tom, as well as the eminences that rose over it, was the sub- 

 ject of a gradual depression ; for little or no alteration ap- 

 pears to have taken place at the time in the relative levels 

 of the higher and lower portions of the sinking area : the 

 features of the land in the northern part of the kingdom, from 

 the southern flanks of the Grampians to the Pentland Frith, 

 seem to have been fixed in nearly the existing forms many 

 ages before, at the close, apparently, of the Oolitic period, and 

 at a still earlier age in the Lammermuir district, to the south. 

 And so the sea around our shores must have deepened in the 

 ratio in which the hills sank. The evidence of this process 



* That similarity of condition in which the hazel and the harder cerealia 

 thrive was noted by our north-country farmers of the old school, long ere 

 it had been recorded by the botanist. Hence such remarks, familiarized 

 into proverbs, as " A good nut year's a good ait year ;" or, " As the nut fills 

 the ait fills." 



