'J30 



SCIENCE. 



[N. S. Vol. XXIII. No. 599. 



The statistical method in chemical g^eol- 

 ogy was a development of his earlier work 

 upon the relative abundance of the chem- 

 ical elements. The average composition of 

 the igneous rocks, as computed by Clarke 

 and others, was compared with that of the 

 sedimentaries. It was shown that in the 

 decomposition of the igneous rocks, and 

 the reconsolidation of the detrital products, 

 the new rocks vi^ould consist of about 

 five per cent, limestones, fifteen per cent, 

 sandstones and eighty per cent, silicates, 

 roughly classed together as shales. It was 

 also shown that all of the sodium in the 

 ocean and the sedimentaries would be fur- 

 nished by the decomposition of a shell of 

 igneous rock, completely enveloping the 

 earth, less than one half mile thick. We 

 thus have a statistical estimate of the total 

 mass of the sedimentary rocks, and the pro- 

 portions of their chief classes. Dr. Clarke 

 also discussed, briefly, some of the uses 

 which had been made of his former aver- 

 .age for the igneous rocks, especially by 

 Van Hise and by Joly. His criticisms 

 -were directed towards conservatism, and 

 against drawing larger conclusions from 

 the figures than their accuracy would war- 

 rant. The data need to be much more 

 fully developed before any large use can 

 be made of them. 



On a Possible Reversal of the Deep-sea 

 Circulation and its Effect on Geological 

 Climates: Professor Thomas C. Cham- 

 BEBLiN, of Chicago. 



The preservation of a narrow range of 

 temperature and a limited variation of at- 

 mospheric constituents throughout the mil- 

 lions of years of the biologic past was es- 

 sential to organic evolution. Continued 

 preservation for millions of yeai*s to come 

 seems equally a condition precedent to an 

 intellectual and spiritual evolution com- 

 mensurate with the physical and biological 



evolutions that have preceded it. It has 

 been customary to assign to the primitive 

 earth a climate quite beyond the Miltonian 

 conception of Gehenna in its fiery intensity 

 and to forecast a final refrigeration 

 scarcely inferior in its antithetic intensity. 

 This is deduced from a gaseous nebula con- 

 densing through gravitation. Such a der- 

 ivation has seemed to some of us incon- 

 sistent with the dynamics of the present 

 solar system and an alternative view has 

 been developed. This view involves a slow 

 growth of the atmosphere to about its pres- 

 ent volume, after which it was controlled 

 by opposing agencies which maintained the 

 narrow limits requisite. The agencies of 

 restraint are molecular velocities, chemical 

 combination and condensation. By virtue 

 of the first, the lighter constituents are re- 

 duced to a minimum and all constituents 

 are restricted within certain large limits. 

 By virtue of the second, the chemically 

 active factors are kept down to states of 

 dilution compatible with organic evolution, 

 while the inert elements have probably been 

 permitted to increase steadily. By the 

 third, the excess of water-vapor has been 

 condensed into the ocean, which has prob- 

 ably increased rather than diminished 

 through the ages. The postulated agencies 

 of atmospheric supply are accessions from 

 without and emanations from within, of 

 which Vesuvius is just now giving us an 

 impressive illustration. 



Subsidiary to this control within narrow 

 limits, pi'onouneed variations must be rec- 

 ognized. In most geologic periods warm 

 climates seem to have prevailed as high as 

 70° and 80° of latitude. How life of 

 subtropical types could have survived the 

 long polar nights is one of the most ob- 

 durate puzzles of the earth's climatology. 

 But hetiveen the warm polar stages there 

 were episodes of glaciation in strangely 

 low latitudes. Extensive glaciation oc- 



