52 Prof. Geiliie—The Old Man of Hoy. 



cliifs in detail, that the true nature and history of the threefold bars of 

 the Old Man can be made out. The yellow and red sandstones are 

 then found to present the ordinary characters of the Upper Old Eed 

 Sandstone, to which they are with probability referred, though as 

 yet they have yielded no fossils. Irregularly^ alternating in thick and 

 thinner beds, they are rent by innumerable perpendicular joints. 

 By means of these divisional lines, slice after slice falls away from 

 the face of the cliifs, which thus maintain their precipitous front 

 towards the Atlantic. Except in regard to their scenic features, 

 these sandstones, however, are less full of interest than the two bars 

 of the Old Man's pedestal. The upper bar consists of a band of 

 dark amygdaloidal lava with a slaggy surface. The same rock 

 appears elsewhere, rising out from beneath the sandstones of the 

 precipices, particularly at the north-western headland, where it con- 

 sists of three or more distinct bands with well -stratified volcanic 

 tuffs. To the north-east of that headland, on a tract of lower ground 

 intervening between the base of the hills and the edge of the sea, 

 several well-marked volcanic " necks " or pipes occur, representing 

 some of the vents from which the streams of lava and showers of 

 ash were poured. The complete interstratification of the beds of 

 erupted material with the lower portion of the sandstones proves that 

 the volcanic action showed itself at the beginning of the deposition 

 of the Upper Old Eed Sandstone in this region. Another little vent 

 may be observed on the Caithness coast, near John o' Groat's House ; 

 perhaps some may still remain to be noticed among the central and 

 northern members of the Orkney Islands. It seems to have been a 

 singular and local outburst of volcanic energy during Upper Old 

 Eed Sandstone times — the only one yet discovered to the north of 

 the Highlands. The uppermost bar then of the pedestal on which 

 the Old Man has taken his stand is a massive sheet of lava. 



The lower bar belongs to a very different period, and has a totally 

 dissimilar history. On looking more closely into the strata which, 

 even seen from the sea, plainly lie unconformably below the lava 

 and its overlying sandstones, we find that they consist of dark thin- 

 bedded sandstones, shales and impure limestones. In short, they 

 are a portion of the great series of deposits known as the Caithness 

 flagstones. On many of their exposed surfaces shining jet-black 

 scales, bones and teeth of the characteristic fishes of these flag- 

 stones may be noticed. "What a suggestive picture of the imper- 

 fection of the geological record is presented to us by some of these 

 weather-beaten or surf- worn sheets of rock ! We pick up from 

 their crannies the broken whelks, nullipores, and corallines, tossed 

 up by the last storm from the zones of life now tenanting the sea 

 below us. The limpet and sea-anemone, the whelk and barnacle, 

 are clinging to the hardened sand over which the Osteolejpis and 

 Coccosteus and their bone-cased brethren disported in the ancient 

 northern lake of Lower Old Eed Sandstone times. Nay, we may 

 now and then watch a living mollusc creeping over the cuirass of a 

 palfeozoic fish. Yet who can realize the lapse of time which here 

 separates the living from the dead ? 



