438 
practical point of view. The progress made 
in all branches of the work, although com- 
paring favorably with the operations of pre- 
vious years, has not been as apparent as 
usual on account of many pieces of patch 
work made necessary by the rapid strides in 
the past. The work across the peninsula 
of Florida from Fernandina to Cedar Keys 
was broken off at the beginning of the Civil 
War and remained untouched until last 
winter. It will be completed during the 
coming season. The Transcontinental Are 
begun in 1871 has just been completed by 
the direct chain of triangulation from 
Washington to Cape May, thus cutting off 
the older and less reliable work by way of 
Delaware Bay. This work, of the highest 
‘ importance in international geodesy, to- 
gether with the completion of the oblique 
are from Maine to Mobile, already men- 
tioned, marks an era in American geodesy 
and contributes new and valuable informa- 
tion as to the size and shape of the earth. 
Pe. 
CURRENT NOTES ON PHYSIOGRAPHY. 
THREE DRIFT SHEETS OF IOWA. 
THE work of Calvin on Iowan drift is 
continued by Bain (lowa Geol. Survey, 
VI., 1896, 429-476), whose report is of 
much geographical interest. The Kansan 
drift forms the surface of rather more than 
the southern half of the State ; it is deeply 
weathered, the granite boulders being badly 
rotted and the limestone leached out; the 
surface is well carved by streams and holds 
no lakes. The Iowan drift occupies some- 
what less than the northern half of the 
State; it is also well dissected, but less 
completely than the Kansan, and sloughs 
remain here and there on its surface. No 
moraine is found along its margin; but ex- 
tensive loess deposits are spread forward 
from it over the dissected surface of the 
Kansan sheet. The Wisconsin drift is well 
developed in a strong lobe that invades the 
SCIENCE. 
[N. S. Voz. VI. No. 142. 
State to a little south of its center, and 
thus overlaps both the older sheets. Its 
surface is much less dissected by valleys, 
and many lakes remain upon it. Its border 
is marked by a strong moraine, from which 
extensive gravel trains are prolonged down 
the outer valleys. The diversity of the 
- glacial period and the considerable value of 
inter-glacial epochs thus find much support 
from the Iowan geologists. 
A special discussion of erosion curves 
accompanies the account of the Kansan 
drift topography ; and it is pointed ont 
that many of the rivers of to-day, although 
occupying valleys carved in the drift, 
nevertheless follow preglacial or intergla- 
cial courses, and are therefore to be called 
resurrected, following McGee’s use of this 
term. 
MOUNT ST. HELENS. 
Liszut. C. P. Exxriorr, U.S. A., gives an 
interesting account of Mount St. Helens 
(Nat. Geogr. Mag., VIII., 1897, 226-230), 
from which many items appropriate to its 
class may be gathered. The mountain 
stands west of the Cascade range divide, its 
truncated cone reaching a height of 8,608 
feet. Its scopes have been dissected by ra- 
vine streams and repaired by lava streams, 
the latter often interfering with the escape of 
the former and producing lakes and swamps. 
The ravines have the radial course usual 
on dissected voleanoes. The flows of lava 
and volcanic sand descend from near the 
mountain summit, running around hills asa 
river passes islands, and ‘filling up the 
country’ in their course. Spirit lake, five 
miles northeast of the summit, occupies a 
valley dammed by sand, ashes and pumice, 
which are there very plentiful. A flow that 
descends five miles to the southwest of the 
summit first nearly fills in the depression 
toward Green buttes; then passing around 
the buttes, the lava unites and fills in be- 
tween Goat mountain and a ridge northeast 
