454 D. MACKINTOSH ON THE ERRATIO BLOCKS OF 
Discussion. 
Prof. Ramsay spoke of the value of these detailed observations. 
He thought that both land-ice and floating ice were concerned in 
the distribution of erratic boulders, and in many cases these boulders 
rested on striated surfaces. There were many boulders in Anglesey 
which had travelled from the north. Most of the northerly stria- 
tions, he thought, could only be produced by an ice-sheet from 
the north. Still he had no doubt that there were also floating 
bergs, as in Cheshire, where boulders were associated with marine 
shells. 
Prof. .Hvenes had had the pleasure of accompanying Mr. 
Mackintosh in the field, and testified to the painstaking care with 
which he gathered information. He thought the facts observed were 
best explained on the view that, during the period of extreme gla- 
ciation in N.W. Europe, the Scandinavian ice overrode every thing ; 
when the cold had abated, and the mountain-ranges had sunk, the 
Scotch ice pressed out on all sides, encroaching on England and 
Wales. Next the glaciers of the Lake-district had their own deve- 
lopment, pushing against the mountains of North Wales so that the 
Welsh ice could not travel out along the northern valleys; in con- 
firmation of which he poimted out that the traces of the most 
ancient glaciation ran, irrespective of level, over hill and dale to the 
east. During all these periods the sea followed the receding ice as 
submergence went on; but the drift with flints, such as is found 
at various levels all round Wales, belonged to a later period and 
to different conditions. 
Prof. Boynuy stated that he had examined a collection of boulders 
wade by Mr. Crosskey from near Birmingham, and could confirm 
Mr. Mackintosh’s determination of the three origins of the boulders. 
He thought that many felstones could be identified, and that the 
crossing of the boulders could only be explained by floating ice. 
He could not understand how, if ice came down to Wales from 
Scandinavia or Scotland, Wales also should not have had glaciers large 
enough to keep the northern ice at a distance from the mountains. 
Dr. Hicks expressed his agreement with the author. In Pem- 
brokeshire foreign rocks were present, apparently coming from the 
north—he thought, the result of floating ice. Land-glaciers would 
bring boulders down to the sea, and they would be drifted away 
by floating ice and currents. 
Prof. Ramsay said that he had not asserted that the ice covered 
Pembrokeshire, so that Dr. Hicks’s criticism did not apply. 
Dr. Hicks explained that striated rock-surfaces and boulders 
were common in Pembrokeshire. These he looked upon as evidences 
of local glaciers previous to the floating-ice period. 
Prof. Srrrzy referred to the correlation of the drifts proposed by 
Mr. Mackintosh. He thought we could not assume that the surface 
had kept the same level above the sea, but that the glacial phe- 
nomena were due to the elevation of the north of Europe; and as 
