38 
PETROLOGY: G. P, MERRILL 
percentages of actually observed falls and the relative basicity of their mate- 
rials. The results of such consideration are given below:^ 
Of the total 367 known meteoric irons there were seen to fall but 17, or 
less than 5%. These are essentially metallic; ultra basic. 
Of the 31 known stony irons variously classed as Lodhranites, Pallasites 
and Mesosiderites, carrying at times as high as 50% metal, there were seen 
to fall but 5, or in round numbers 16%. 
Of the 370 known stones composed mainly of silicate minerals, with chon- 
dritic structure, carrying from 5 to 25% metal (Howarditic chondrites to 
Ureilites inclusive), there were seen to fall 322, or 87%. 
Of the 21 calcium-aluminum-rich stones, carrying less than 1% metal, free 
of chondrules, and variously classed as Angrites, Eukrites, Shergottites and 
Howardites, there were seen to fall 20, or 95%. 
Of the 12 magnesia rich stones essentially free from metal without chon- 
drules and classed as Bustites, Chassignites, Chladnites and Amphoterites, the 
most acidic types known, there were seen to fall 12, or 100%. 
As there is little reason for supposing that falls of one kind are not as con- 
spicuous as those of another, it would seem a fair assumption that those of 
which the seen percentage was the smallest were the earliest, perhaps largely 
prehistoric.^ Hence arises the thought of a gradual decreasing basicity or 
what is the same thing, increasing acidity of accumulated materials, as time 
goes on. While it would seem absurd to claim that such a change could 
manifest itself perceptibly during the few years of observation, it is neverthe- 
less worthy of note that, however much uncertainty is attached to the period 
of fall of upwards of 95% of the known meteoric irons, the stones of the last 
two classes mentioned, which are of the most acidic type and with one or two 
exceptions are iron free, have fallen within a period of a little more than 
one hundred years. 
Following out the same line of thought, it would seem possible that the 
thousands of meteors which are known to enter our atmosphere daily and 
yet leave no record of their fall, might be products of a still further differ- 
entiation of cosmic matter (or perhaps derived from an entirely different 
source) and of such eminently combustible material as to be largely consumed 
in their flight. 
Additional interest is attached to this suggestion from the fact that there 
are known but eight carbonaceous meteorites, i.e., eight stones in which an 
uncombined carbon (or possibly hydrocarbon) occurs in such quantities as to 
give them a distinctive character and which, therefore, might be considered 
liable to destruction by heat while passing through our atmosphere. All of 
these eight were seen to fall, the first, that of Alais, France, in 1834 and the 
latest, that of Indarch, India, in 1891. 
It is possible to account for some of the facts here given on the assumption 
that many meteorites are of an extremely perishable nature, and unless seen 
to fall and sought for immediately, likely to become destroyed through dis- 
