TRANSACTIONS OF THE SECTIONS. 95 
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Further, the colour of the mud or clay would correspond, as in the thoroughfare or 
public road, with the colour of the rocks or stones which had been ground down to 
form it. Now for rafts of wood we have but to substitute rafts of ice, a submerged 
land, covered by many fathoms of sea, for the shallows of the river, and some powerful 
ocean-current, such as the Gulf or Arctic Stream, for the river itself, and we at once 
arrive at a theory of the boulder clay and its origin, which seems to account more 
satisfactorily for the various phzenomena of the deposit than any of the others. It is 
a theory that plays so easily along the intricacies of the various wards of the locked 
mystery, that Mr. M. had come to regard it as the true key. 
There is a peculiar kind of clay which forms on the surface of a hearthstone 
or piece of pavement under the hands of a mason’s labourer engaged in rubbing 
it smooth with water and a polisher of gritty sandstone. It varies in quality and 
colour with the character of the stone; a flag of Arbroath pavement yields a bluish- 
coloured clay ; a flag of the lower old red sandstone, a reddish-coloured clay; a flag 
of Sutherlandshire oolite or of the upper old red of Moray or Fife, a pale yellowish 
clay. The polishing process is a process which produces clay out of stones as various 
in tint as the colouring of the various stones which yield it ; and in almost every 
instance does the clay thus formed resemble some known variety of the boulder clay. 
The boulder clay, in the great majority of cases, is in colour and quality just such a 
clay as might be produced by this recipe of the mason’s labourer from the rocks on 
which it rests. The red sandstone rocks of Cromarty, Moray, and Ross, are covered 
by red boulder clay, and a similar red boulder clay overlies the red sandstone rocks 
of Forfarshire. Again, in the middle and north-western districts of Caithness, where 
the prevailing flagstones render the average tint of the rock a sombre gray, the 
boulder clay assumes, as in the neighbourhood of Wick and Thurso, the leaden colour 
of the bed which it overlies ; while over the coal-measures of the south of Scotland, 
as in East and West Lothian and around Edinburgh, it is of a bluish-black tint—ex- 
actly the colour which might be anticipated on the polishing theory from the large 
mixtures of shale-beds, coal-seams and trap rocks which occur amid the prevailing 
light-hued sandstones of the deposits beneath. 
Another circumstance specially worthy of remark, is the general direction of the 
grooves and scratchings on the dressed surfaces of the rocks in situ. With slight 
divergences in various localities towards the south or north, they run generally from 
west to east; and this westerly direction seems to be exactly that, which, reasoning 
from the permanent phznomena of nature, might be premised. There must have 
been trade-winds in every period of the world’s history in which the earth revolved 
from east to west on its axis, and with trade-winds the accompanying drift-current ; 
and of consequence, especially ever since the existence of a great western continent, 
Stretching far from south to north, there must have been also a Gulf-stream. The 
water heaped up against the coasts of this western continent at the equator by the 
drift current ever flowing westwards, must have been always, as now, returning east- 
wards in the temperate zone, to preserve the general level of the ocean’s surface. 
Ever, too, since winter took its place among the seasons there must have been an 
Arctie current. The ice and snows of the higher latitudes that accumulated during 
the winter must have again melted in spring and early summer, and a current must in 
consequence have set in as the seasons of thaw came on, just as we now see such a 
current setting in, in those seasons in both hemispheres which bears the ice of the 
Antarctic circle far towards the north, and the ice of the Arctic circle far towards the 
south, The point at which, in the existing state of things, the Gulf-stream and the 
Arctic current come in contact, is that occupied by the great bank of Newfoundland, 
and by some the very existence of the bank has been attributed to their junction and 
to the vast accumulations of gravel and stone cast down year after year where these 
two great tides meet and jostle. That the point where the Gulf and Arctic currents 
come in contact should now lie so far to the west, is a consequence of the present 
disposition of the Arctic and western continents—perhaps, also, of the present posi- 
tion of the magnetic pole. A different place and disposition would give a different 
point of meeting, and it is as little improbable that they should have met in the remote 
past some two or three age ἐν miles to the west of what is now Scotland, as that 
in the existing period they should meet some two or three hundred miles to the east 
of what is now Newfoundland. The northern current would be deflected by the 
