A SUMMER RAMBLE AMONG THE HEBRIDES. 187 



ral arrangement from west to east, along the northern coast 

 of Caithness, of the Lower Old Red Sandstone. The great 

 Conglomerate base of the formation we find largely developed 

 at Port Skerry, just where the western boundary line of the 

 county divides it from the county of Sutherland ; its thick 

 upper coping of sandstone we see forming the tall cliffs of Dun- 

 net Head ; and the greater part of the space between, nearly 

 twenty miles as the crow flies, is occupied chiefly by the shales, 

 grits, and flagstones, which we have found charged so abun- 

 dantly with the strangely-organised ichthyolites of the second 

 stage of vertebrate existence. In the twenty intervening 

 miles there are many breaks and faults, and so there may be, 

 of course, recurrences of the same strata, and re-appearances 

 of the same beds ; but, after making large allowance for par- 

 tial foldings and repetitions, we must regard the development 

 of this formation, with which the twenty miles are occupied, 

 as truly enormous. And yet it is but one of three that oc- 

 cur in a single system. We reach the long flat bay of Dun- 

 net, and cross its waste of sands. The incoherent coils of 

 the sand-worm lie thick on the surface ; and here a swarm of 

 buzzing flies, disturbed by the foot, rises in a cloud from some 

 tuft of tangled sea-weed ; and here myriads of gray crustaceous 

 sand-hoppers dart sidelong in the little pools, or vault from 

 the drier ridges a few inches into the air. Were the tri- 

 lobites of the Silurian system, at one period, as their remains 

 testify, more than equally abundant, creatures of similar 

 habits 1 We have at length arrived at the tall sandstone pre- 

 cipices of Dunnet, with their broad decaying fronts of red 

 and yellow ; but in vain may we ply hammer and chisel 

 among them : not a scale, not a plate, not even the stain of 

 an imperfect fucoid, appears. We have reached the upper 

 boundary of the Lower Old Red formation, and find it bor- 

 dered by a desert devoid of all trace of life. Some of the 

 characteristic types of the formation re-appear in the upper 



