1Q2 REVIEWS 
The petrography of the pre-Cambrian rocks is discussed, and num- 
erous analyses of granites, syenites, gneisses, and amphibolites are given. 
GN, dis 18e 
An Excursion to the Yosemite (California), or Studies in the For- 
mation of Alpine Cirques, ‘‘Steps,’ and Valley “Treads.” By 
E. C. ANDREWS. Jour. and Proc. of the Royal Society of 
IN2 S: Wales, XG. 262-275)" igss 17 
Considerable space is given to The Psychological Factor in the History 
of the Glacial Controversy in which is emphasized the necessity of inter- 
preting glacial features by the ice floods that formed them, and not by 
the present dwarfed representatives of those floods. The dynamics of 
ice stream erosion is discussed with special emphasis on the effects of 
ice falls and their recession forming “steps” and ‘‘treads,’”’ and on the 
formation of cirques and roches moutonnées. 
Previous to glacial times, the Merced and Tenaya rivers had a fairly 
even descent through the Yosemite region, with a notable constriction in 
the valley between El Capitan and the Cathedral rocks. Later, with 
the ice moving through this constriction, the velocity at this point was 
increased, and, likewise, the erosive power, which developed a “‘step”’ 
with ‘“‘basined tread.”” The “step” and “tread,” once formed, were 
rapidly enlarged by recession through the processes of sapping and 
quarrying, and in their recession left hanging valleys, now marked by 
water falls. 
Avvkaais 
Department of Terrestrial Magnetism of the Carnegie Institution 
of Washington, Annual Report of the Director. By L. A. 
BaveEerR. Year Book No. 9, pp. 195-204; Pl. 1. 
In a general summary is given the work done with the ‘‘ Carnegie” 
in correcting magnetic charts, and an outline of her present circum- 
navigation cruise. The field work in the various countries, the ocean 
work of the “‘Carnegie,”’ the office work, and the shopwork accomplished 
during the year are stated briefly. The map (PI. 5) accompanying the 
report shows the status of the magnetic work accomplished both on 
land and sea up to October 31, tg10, and the uncompleted portion of the 
present cruise of the “ Carnegie.”’ 
Arco B. Et 
mcrae 
