172 
IOWA ACADEMY OF SCIENCE 
Moreover, a dry climate appears to prevent rapid rock-decay. There 
is practically no such phenomenon as chemical decomposition of the rocks 
as it is known in the moister regions of the globe. The breaking down of 
rock-masses near the surface takes place mainly by means of insolation, 
which is strictly mechanical disintegration. Meteoric irons remain for 
years upon the surface of the desert without notable oxidation. 
Again, the meteorites in such regions, instead of being immediately 
lost to view in vegetation, covered by soil, and subject to rapid chemical 
decay, as in humid countries, are left exposed on the surface of the 
ground through the constant removal by the winds of the lighter soils. ^ 
This cause affects, of course, all the larger rock-fragments, of whatever 
origin. The pebble mosaics which cover large tracts of arid plain, de- 
scribed by Blake,i by Tolman,+ and by me,|| amply attest the extent of 
this remarkable phenomenon. 
For peculiar reasons, meteoric masses are not easily recognizable in the 
pebble pavements. The majority of desert rocks are susceptible to not- 
able discoloration and wind-polishing, which imparts to them a burnt and 
fused appearance. Travelers in the desert are prone to ascribe this char- 
acteristic of the rocks to volcanic action ; and it is invariably one of the 
features of such regions which at once atttracts their attention. For ex- 
ample, in describing the general impressions gained in crossing the broad 
desert tract in New Mexico known as the Jornado del ]\Iuerto, Wallace^ 
says, ‘Hhe portion I speak of appears to have served its time, worn out, 
been dispeopled and forgotten ; the grass is low and mossy, with a perish- 
ing look — the shrubs, soap-weed,, and bony cactus writhing like some 
grisly skeleton ; the very stones are like the scoria of a furnace. ^ ’ Until 
they are broken in two the darkened rock-fragments give little suggestion 
of their real lithologic character. 
The more basic rock-masses and larger rock-fragments which strew 
the ground throughout the arid regions are almost invariably^ coated by a 
black iron and manganese film which, highly polished by the wind-blown 
sands and dusts, gives every appearance of fusion. The aspect thus pro- 
duced is not unlike that of the f used*' surface of meteorites falling in moist 
lands. Among such dark lacquered rock-fragments, it is with greatest 
difficulty that true meteorites can be distinguished. That they do oc- 
cur abundantly nevertheless, is well shown by the rock-collections dis- 
played at fevery cattle ranch. 
Bull. Geol. Soc. America, Vol. XIX, p. 73, 1908. 
•fTrans. American Inst. Mining Eng., Vol. XXXIV. p. 161, 1904. 
tJournal of Geology, Vol XVII, p. 149, 1909. 
II Ibid, p. 74. 
§Land of the Pueblos, p. 140, 1888. 
