GAY GULCH AND SKOOKUM METEORITES, 
1 
to Pliocene time at least and that their actual descent antedates 
even this period. 
CONCLUSION. 
While the evidence may not be entirely conclusive there is 
much to support the theory that these two meteorites are 
individuals belonging to a single shower. That they can be 
detached fragments of a single mass reaching the earth as such 
seems out of the question; a glance at the diagram will show that 
any natural movements to which they have been subjected since 
reaching the earth would tend to bring them nearer together. 
On the other hand an examination of the contours as outlined 
on the diagram will show that it is highly improbable that the 
distance between the points of contact could have been greater 
than 10 miles, an interval which has been greatly exceeded in 
the case of some observed showers. The strongest evidence 
of the identity of the two meteorites rests, however, with their 
general structure and composition. They both belong to a 
comparatively limited series of nickel-rich meteorites. Of 215 
iron meteorites whose analyses are quoted by Farrington 1 only 
58 showed nickel-cobalt contents of 10 per cent or over. The 
difference of 4-08 per cent is not greater than that sometimes 
found to exist between the nickel-cobalt contents of different 
parts of the same mass. The nickel-cobalt content of Shingle 
Springs has been shown to vary from 8*88 per cent to 17*17 per 
cent; that of the Troost iron (Babbs Mill) from 9*76 per cent to 
19 per cent; that of the Blake iron (Babbs Mill) from 7*95 per 
cent to 14*24 per cent; that of Illinois gulch from 6*86 per cent 
to 13*48 per cent. In their general structure they present 
certain features common to both which seem unique among 
nickel-rich irons: their tendency to follow a definite crystallo- 
graphic arrangement constitutes in particular a most unusual 
property in meteorites of this kind. They both exhibit the same 
peculiar cloudiness and chatoyancy. A comparison of the 
photomicrographs (Plates II, III, X, and XI) will show the 
Analyses of Iron Meteorites, compiled and classified, Field Columbian 
Museum, Chicago, Vol. 3, No. 5. 
