808 B. N. PEACH AND J. HORNE ON THE 
the smallest hollows and overflowing the projecting knobs of rocks, 
indicating in an unmistakable manner that the agent must have 
pressed steadily and firmly over the whole area. °N ay, more, the 
islands have been grooved and striated in one determinate direction, 
while rocky slopes have been likewise abraded; and from the 
manner in which the strize run obliquely up the hill- face, it is evident 
that the agent must have ascended the slopes, and ultimately over- 
flowed the high grounds. Now it is hardly necessary to point out 
that neither “coast- -ice nor icebergs are capable of producing such 
results as these. It is impossible - to conceive that icebergs or coast- 
ice could press steadily on a wide archipelago like Shetland, so as to 
plane down the inequalities on the surface; far less could they 
produce this uniform system of striation. We may well ask, by 
what means could floating ice or coast-ice ascend a rock-slope 
several hundred feet high, leaving at the same time indelible im- 
pressions of the upward movement ? Such an cccurrence would be 
a physical impossibility. 
~ Again, the phenomena of the Boulder-clay are quite at variance 
with the floating-ice theory ; for if this deposit be due to the drop- 
pings of icebergs or coast-ice, then assuredly it would have been 
more or less stratified ; whereas, from one end of Shetland to the 
other, the Boulder-clay, with but few exceptions, is quite amor- 
phous. If it be really a marine deposit, how could it possibly par- 
take of the characters of the rock-formation on which it rests, and 
how could the relative ingredients diminish in number in propor- 
tion to the distance from their parent source ? 
Further, the occurrence of blocks in the Boulder-clay on the 
western sea-board of Unst and the Mainland, which must have crossed 
the watershed to reach their present position, is still less explicable 
by this hypothesis. For if the high grounds of Unst or the Main- 
land were submerged so as to allow a free passage for icebergs in 
their westward career, where are the areas of gabbro, serpentine, or 
Old Red Sandstone which could have supplied the materials found 
in the Boulder-clay ? Even if we suppose that ice rafts drifted off 
the eastern sea-board laden with such materials, we must suddenly 
invoke a special subsidence of several hundred feet at least, both 
in Unst and in the Dunrossness area, to enable them to cross the 
watershed. But this improbable supposition still leaves unexplained 
the relationship which exists between the relative distribution of 
the stones in the Boulder-clay on the west coast, and the relative 
areas occupied by the rock masses. or these reasons, therefore, 
and others which it is not necessary to specify, it is impossible to 
reconcile the glacial phenomena of Shetland with the theory of ice- 
bergs or coast-ice. 
3. Shetland glaciated by Scandinavian Ice.—Similar phenomena 
to those now referred to have been observed and described again 
and again in Scotland and other highly glaciated regions, where they 
have been almost universally ascribed to the action of land-ice. 
It is not necessary for us to show how the uniform system of stria- 
tion, or the rounded outlines, or the close relation between the 
Boulder-clay and the rocks on which it rests, are satisfactorily ex- 
