302 RAMBLES OF A GEOLOGIST. 



bogs cease. The chain of green bogs is a consequence of the 

 stratum of permeable sand. I have in vain sought this an- 

 cient layer of sand, decidedly of the same era with the ar- 

 gillaceous bed which overlies it, for aught organic. A sin- 

 gle shell, so unequivocally of the period of the boulder-clay 

 as to occur at the base of the deposit, would be worth, I have 

 said, whole drawerfuls of fossils furnished by the better-known 

 deposits. But I have since seen in abundance shells of the 

 boulder-clay. 



There is another scenic peculiarity of the clay, which the 

 neighbourhood of Cromarty finely illustrates, and of which 

 my walk this morning furnished numerous striking instances. 

 The Giants' Graves to borrow from the children of the 

 place occur on the steep slopes of the old coast line, or in 

 the sides of ravines, where the clay, as I have said, had once 

 presented a precipitous front, but had been gradually moulded, 

 under the attritive influences of the elements, into series of 

 alternating ridges and furrows, which, when they had flat- 

 tened into the proper angle, the green sward covered up from 

 further waste. But the deep dells and narrow ravines in 

 which many ranges of these graves occur are themselves pe- 

 culiarities of the deposit. Wherever the boulder-clay lies 

 thick and continuous, as in the parish of Cromarty, on a slop- 

 ing table-land, every minute streamlet cuts its way to the 

 solid rock at the bottom, and runs through a deep dell, either 

 softened into beauty by the disintegrating process, or with all 

 its precipices standing up raw and abrupt over the stream. 

 Four of these ravines, known as the " Old Chapel Burn," the 

 "Ladies' Walk," the "Moral's Den," and the "Red Burn," 

 each of them cutting the escarpment of the ancient coast line 

 from top to base, and winding far into the interior, occur in 

 little more than a mile's space ; and they lie still more thick- 

 ly farther to the west. These dells of the boulder-clay, in 

 their lower windings, for they become shallower and tamer 



