in Europe and North America. 325 
of Monthey, in the valley of the Rhone, and the great erratic 
boulders that strew the southern flank of the Jura had been 
transported by icebergs derived from glaciers which descended 
in the Alpine valleys to the sea-level, during a period of sub- 
mergence in which the low country that lies between the Jura 
and the Oberland was covered with erratic drift. 
_+here was nothing new in this latter opinion, for it had pre- 
viously been held by several distinguished geologists, both 
English and continental. 
Since then I have twice revisited Switzerland, and have seen 
800d reason to change my opinion respecting the cause of the 
ort of erratic blocks to Monthey and the Jura, and of 
débris not remodelled by rivers, &c., that lies scattered over the 
many persons in England who doubt these conclusions, it may 
hot be beside the question to state the considerations that led 
me to reject the old theory. 
ons for abandoning the older theories.—I first began to doubt 
the correctness of my earlier opinions in the summer of 1860, 
While examining the country near 
Selle, and the Eifel. Neither in the valleys nor on the wide 
table-lands on both sides of the Rhine and’ the Moselle is there 
el sign of glacial drift. Excepting alluvial débris in the val- 
’ fl fre- 
ily rounded, polished, and striated the rocky banks in the 
tion of the flow. Boulders, transported from further up 
the stream, also sometimes lie on the shores. But, in the ab- 
Same absence of marine drift prevails. There, looking eastward 
towards the Rhine, the mountains, chiefly of gneiss, are wonder- 
Y scarred, telling the observer of the wasting effects of 
AM. Jour. Sct.—Snconp Series, Vou. XXXV, No. 105.—Mayr, 1863. 
42 
