OF ELIE AND EREOL. 631 



inference to the two deposits as a whole. If we endeavour to picture the time 

 when the shell-clay was laid down, it will be plain that all through it there must 

 have gone on the process of the formation of the boulder-clay. We can tell to a 

 certainty that the greater portion of Scotland was above water when the Elie and 

 Errol shells lived, for the characteristic species, the Leda truncata, does not live 

 in more than 50 fathoms of depth. A great part of the country, therefore, stood 

 out of the water, and all over the higher grounds the great ice-sheet was doing 

 its work, in forming the boulder-clay. When the shells lived in the Elie clay, 

 the glaciers were scouring the valleys of the Pentlands, and rising over the sides 

 of Arthur's seat. When the current swept the sea-beds of Errol, the ice-sheet 

 was grinding the flanks of Benvoirlich, and ploughing its way down the solitudes 

 of Glenartney. This is the story of that epoch, which admits of no denial. There 

 was land, and there was sea, and the two formations were cotemporaneous — 

 the Arctic shell-clay under the sea, and the boulder-clay on the land. Take any 

 portion of the shell-clay, and you would probably find that if the whole facts could 

 be brought out, some portion of the boulder-clay was prior, some cotempo- 

 raneous, some posterior to it. But as a whole, the two were simultaneous. As 

 surely as there was land and sea, so the land and the sea formations ran on side 

 by side, just as the two processes may be seen this day going on side by side at 

 Greenland or Spitzbergen. 



2. Then a second question is, whether the boulder-clay is or is not fossiliferous ? 

 Some have been inclined to view it as marking a time of dreariness and desolation, 

 almost as azoic, a period of death, so devoid is it of fossils. This, I believe, is a mis- 

 take. If we use the term boulder-clay in a mineralogical sense for a certain clay in 

 a certain mechanical state, then, as a whole, it is unfossiliferous, and we have seen 

 why it must be so. But if we use it in a geological sense as representing a par- 

 ticular epoch, then the fossils of this Arctic shell-clay are the fossils of the boulder- 

 clay. In them we have the marine life of the boulder-clay period. The fossil 

 fish of the Old Red Sandstone belong to their own epoch, none the less that the 

 bed in which they are found may not be sandstone and not red, and in this 

 sense the fossils of the Arctic clay might be termed boulder-clay fossils, as repre- 

 senting the marine life of that epoch of which the boulder-clay was the great 

 feature. Having thus glanced at the details of the different deposits, let us now 

 advert to the 



General Results. 



The only safe rule in classifying the beds of any geological epoch is by the 

 enclosed fossils. Were we to take the boulder-clays, brick-clays, and gravels, 

 and try to work out the succession by the mineral and mechanical structure, we 

 should be groping in the dark. Dr Fleming showed that there are earlier and 

 later boulder-clays ; and this is quite plain, when we contrast that of Errol, under- 



