156 TJie American Geologist. Maich, ]89s 
sent the s^rcater display of ferriferous products. Their develop- 
ment is limited to exposed surfaces. When otherwise than a 
mere speculum, the oxide is characterized b\" prismatic cleav- 
age. Both detritus and float are then particularly rich. Dykes 
in which no prismatic cleavage is pronounced exhibit as a rule 
no more than a coating or specular surface of ferric oxide. 
This holds true with regard to the more expansive intrusions. 
When presented in outliers distinct from the overflow some 
of these are of imposing aspect, bearing semblance to fine 
bodies of ore. The sharp ringing sound from a blow with 
the hammer serves to distinguish such masses, as well as any 
form of their detritus, including even an excellent type of ore 
of like origin, abundantly afforded in places as float. 
From the fact that the iron ores classified in my original 
descriptions as concentrations are essentially superficial, it was 
argued on general grounds that little or no economic value 
could attach to them. So deceptive in appearance, however, 
were some of these occurrences in an unbroken state in the 
year 1884 that several of them had been located by denounce- 
ment, and the critical attention of geologists and capitalists 
confidently invited with a view to development as ore de- 
posits. 
Reference is here made to a subordinate and worthless 
type of ferriferous developments rather than to the character- 
istic class for which the region is renowned, because it serves 
the present purpose of comparison with somewhat analogous 
occurrences which have proved even more deceptive in ap- 
pearance. Both occurrences are, nevertheless, significant of 
one mode of genesis or differentiation of iron ores, namely, 
by residual concentration of iron oxides as a result of weath- 
ering action. 
The second instance referred to is a remarkable differential 
development of ferric and magnetic oxides from an amorph- 
ous basic aggregate in the state of Washington on Cle Elum 
river, one of the tributaries of the Yakima. This fine moun- 
tain stream, which expands into two lakes of the same name, 
distinguished as Upper and Lower, penetrates the more 
mountainous parts of its course in a deep gorge several miles 
long. Mountains on either side rise to elevations of several 
thousand feet. The Cascade range on the west presents tow- 
