360 The Glacial Theory of Prof. Agassiz. 
Von Buch, Escher, and Studer, have shown, from an examination of 
the mineral composition of the boulders, that those on Western Jura, 
11, have come from the region of Mont Blanc, M, and the Valais, V gues 
those on the middle parts of Jura, 22, from the Bernese Oberland, 
and those on Eastern Jura, 3, towards Aargau and Zurich, from 
Alps of the Petits Cantons, P. The blocks have thus been derived from 
the parts of the Alps nearest, generally speaking, to the localities where 
we now find them, as if they had passed across the valley in a direction 
at right angles to its length. 
The blocks are generally angular, and therefore had not been exposed 
to much attrition, either from agitation amidst gravel, or from mutual 
action. Many of them are of prodigious magnitude. © The famous mass 
of Pierre @ Bot, containing 50,000 cubic feet, and weighing probably 
4,000 tons, equals a goodly mansion in size, namely, one of 30 feet in 
front, i in n depth, and 40 in n height. lt rests on a part of Jura 2,177 
the level of the lake of Neu- 
chatel, we: ‘Near Chaumont there is a group of granite blocks, which, 
from their magnitude, their number, and their juxtaposition, look like a 
hamlet of cottages. The large Alpine boulders of Jura, in short, may 
be counted by hundreds, and the small ones by thousands. 
The boulders are distributed in zones on the terraces, which, like the 
steps of ‘a stair, form the out-goings of the different formations. The 
highest are disposed in rings, as in figure 7, round the lower summits 
of Jura, at a height between 3,000 and 3,300 feet above the sea. The 
other zones occur on the terraces below this; the first at elevations 
from 1,900 to 2,400 feet ; the next at 1,600 to 1,800 feet ; and the last 
descends to the level of the lake of Neuchatel, 1,324 feet above the 
Moreover, these travelled blocks penetrate into the transverse 
and into the interior valleys of Jura, and some are even found at the 
back of the chain, near the Doubs.* 
Saussure attributed the transportation of these boulders to a debacle, 
or great current, rushing from the Alps; and Von Buch, finding that one 
‘current would not account for the phenomena, assumed the existence 
of several. But the inadequacy of such explanations is obvious. 
Ay The Alps; J, Mount Fig. 9. 
Jura, with the great valley, | 
fifty miles wide, between 
thei. Fs 
e, The southern declivi- 
ties of Jura, upon which — 
most of the erratic 
