Geological Society. 503 
will at once meet with the general concurrence of geologists; and 
he admits that the study of the phenomena of glaciers in different 
Jatitudes, as well as at different altitudes, together with the exami- 
nation of their different effects where in contact with the sea, will 
introduce many modifications in the consideration of analogous 
phenomena in countries where glaciers have disappeared ; but he is 
prepared to discuss his theory within the limits of observed facts, 
conscious of having searched for truth solely to advance the interests 
of science. 
To avoid useless discussion, he states, that in attributing to the 
action of glaciers a considerable portion of the results hitherto 
ascribed exclusively to that of water, he does not wish to maintain 
that everything hitherto assigned to the agency of water has been 
produced by glaciers ; he only wishes that a distinction may be made 
in each locality between the effects of the different agents; and he 
adds, that long-continued practice has taught him to distinguish 
easily, in most cases, the effects produced by ice from those produced 
by water. 
Proceeding to the consideration of facts, he says the distribution 
of blocks and gravel, as well as the polished and striated surfaces of 
rocks iz sttu, do not indicate the action of a mighty current flowing 
from north-west to south-east, as the blocks and masses of gravel 
everywhere diverge from the central chains of the country, following 
the course of the valleys. ‘Thus in the valleys of Loch Lomond and 
Loch Long, they range from north to south; in those of Loch Fine 
and Loch Awe from north-west to south-east; of Loch Etine and 
Loch Leven from east to west; and in the valley of the Forth from 
north-west to south-east, radiating from the great mountain masses 
hetween Ben Nevis and Ben Lomond. Ben Nevis, in the north of 
Scotland, and the Grampians in the south, are considered by the 
author te constitute the great centres of dispersion in that kingdom; 
and the mountains of Northumberland, of Westmoreland, Cumber- 
land, and Wales; the hills of Ayrshire, Antrim, the west of Ireland, 
and Wicklow, to be other points from which blocks and gravel have 
been dispersed, each district having its peculiar debris, traceable in 
many instances to the parent rock, at the head of the valleys. 
Hence, observes M. Agassiz, it is plain the cause of the transport 
must be sought for in the centre of the mountain ranges, and not 
from a point without the district. ‘The Swedish blocks on the coast 
of England do not, he conceives, contradict this position, as he 
adopts the opinion that they may have been transported on floating 
ice. 
In describing the phenomena presented by erratic blocks and 
gravel, M. Agassiz first insists upon the necessity of distinguishing 
between stratified gravel and mud containing fossils, which could 
not have been accumulated by true glaciers, although the materials 
may have often been derived from them, and unstratified masses, 
composed of blocks, pebbles, and clay. These stratified deposits 
he considers to be of posterior origin to the glacier epoch. The till 
of Scotland, or the great unstratified accumulation of mud and 
