448 D. MACKINTOSH ON THE ERRATIC BLOCKS OF 
caused by a sheet of land-ice which went no further south, and that 
the boulders found between them and the southerly termination of 
the northern drift were transported by icebergs broken off the end 
of the ice-sheet, is opposed by the fact that the levels of the striated 
rock-surfaces which the bottom of the ice must have touched are 
generally not more than 100 feet above the present sea-level (near St. 
Silas’s church, Liverpool, about 160 feet); in other words, the levels 
are so low that the bottom of the icebergs could not have gone over 
the boulder-strewn higher ground further south, some of which reaches 
nearly 800 feet. On the other hand, small icebergs or large masses 
of floating coast-ice, from Kirkeudbrightshire or Cumberland, may 
have reached the spots where the striated rocks are found, while the 
higher ground to the south may have checked their further progress. 
Should it be said that land-ice may have reached as far as the above 
striated area, and that after its disappearance boulders may have 
been carried by floating ice from their parent rocks, it may be replied 
that we have no evidence of the existence of this land-ice, unless the 
striated rock-surfaces can be proved to furnish an evidence; but, on 
the contrary, I think they can be best explained by floating ice. 
2. Age and Origin of the Striated Rock-surfaces around Birkenhead 
and Liverpool.—These surfaces are all flat, or very nearly so, even 
where the rock would evidently have admitted of being rounded. They 
often present the appearance of the previously uneven rock-surface 
having been uniformly planed down or shaved across. Mr. Darwin 
was perhaps the first to make a distinction (in 1842) between rock- 
surfaces glaciated by land-ice and by floating ice, the former showing 
a tendency to be dome-shaped. In North Wales (where Mr. Darwin 
studied the phenomena), and still more in the Lake-district, roches 
moutonnées are coextensive with the other traces of land-ice, and we 
are not justified in assuming the former presence of land-ice where 
they are entirely absent. All the striated and planed rock-surfaces 
around Birkenhead and Liverpool are covered (so far as I have seen) 
with Upper Boulder-clay which, without any change in its character or 
intervening detritus, touches the striated rock-surfaces. The latter 
look as fresh as if they had been formed yesterday ; and these facts 
would seem to point to the conclusion that while the striated surface 
was still submerged the overlying clay was accumulated. 
VIL. Remarks on Locat BovuLpER-DISPERSIONS. 
Boulders have probably been dispersed from either the Delamere 
or Peckforton hills, as (according to Prof. Hull) they are the nearest 
localities from which a very large block of calcareous conglomerate 
I found in Mr. Jones’s clay-pit near Wrexham could have been 
derived. Its course must have crossed that of the Eskdale granite 
with which, in the clay-pit, it 1s associated. Haughmond hill has 
sent off fragments in the direction of Shrewsbury, around which 
they may be found in the lower gravel and Upper Boulder-clay. 
According to Mr. Maw the Wrekin and neighbouring eminences 
