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IOWA ACADEMY OF SCIENCE 
the moving waters. A thorough chemical investigation of the composi- 
tion of these sands would be highly instructive. The common black sands 
of placers appear to be in the main totally distinct ; and their origin is 
usually traceable to decomposing igneous rocks. The metallic sand-par- 
ticles of the desert soils necessarily long resist decay. Should these parti- 
cles prove to be of meteoric origin, the fact would tend to make such esti- 
mates of the annual meteoric augmentation to the earth’s volume as those 
given by Chamberlin and Salisbury'"' ridiculouslj^ inadecjuate. As it is 
their ligures must be vastly too low. 
The petrologic features of meteorites present many suggestive relation- 
ships to those of the igneous rocks of our globe. Among the common ter- 
restrial rock of igneous origin there are usually recognized four main 
groups: the acidic, the neutral, the basic, and the ultra-basic. Among 
earth-rocks those of the last mentioned class are cpiite rare; but in the 
case of stony meteorites the rock species distinguished are very largely 
ultra-basic. Some of these mineralogic aggregates correspond, it is true, 
to some of the most basic of the terrestrial series ; but the cosmical series 
begins with the earthly basic class and continues through the ultra-basic, 
<of which limbergite and peridotite are the chief terrestrial examples, to 
yet unnamed series in which the metals form a larger and larger pro- 
portion. 
So long ago as 1871, Meunierl^ recognized among the meteorites no 
less than 50 distinct lithologic types, most of wiiich he later" described 
the microscopical characters and reported in them a wide range of me- 
tallic elements. 
Among the metals occurring in meteorites are all of those found in the 
common ores. Gold and silver are the only conspicuous metals which do 
not yet appear to be found abundantly in meteorites. There are, ho^vever, 
good reasons why these tAvo metals have not been reported more fre- 
quently; and other reasons why certain other metals seemingly occur 
only sparingly; so that the apparent absence of these elements in the 
composition of knoAvn meteorites does not preclude their derivation from 
this source. 
As is Avell knoAvn, the relative abundance of chemical elements appears 
to be different in the terrestrial and siderial rocks. It is suggested by 
Farrington, 1 1 hoAvever, that there is A^ery good reason for belieAung this 
difference to be apparent rather than real. Only the crust of the earth 
*Geology, Vol. I, p. 381, 1905. 
tGeologie cles Meteorites: Moniteur scientinque Quesneville, Feb. 1-15, 1871. 
de la soc. d’liist. nat. d’Autun, t, XVI, 1893; also t. XVIII, 1895. 
I [Journal of Geology, Vol IX, p. 394, 1901. 
