CRUSTAL DEFORMATION AS THE CAUSE OF CLIMATIC CHANGES. 261 



erally also causes volcanic activity which may be of the quiet type where vast deposits of 

 liquid lava are formed, as happened in the Deccan, or of the violent, explosive type. If 

 explosive eruptions occur, still further chmatic changes may be induced. To this would 

 be added the effect of the great elevation and extent of the land in causing rapid weathering 

 and erosion. Under such circumstances much CO2 is set free from the rocks, and may 

 in time become so abundant as to appreciably raise the earth's temperature. Thus it 

 appears that in our completed hypothesis solar changes stand first in importance. With 

 them, however, and perhaps inseparable from them, occur changes in the earth's interior 

 whereby crustal deformation is induced. This, in turn, is usually associated closely with 

 volcanic eruptions, and rarely takes place without them. It also gives rise to the processes 

 whereby the amount of CO2 is increased. All four tj'pes of activity, solar, crustal, volcanic, 

 and erosional, appear to have a direct effect upon terrestrial climate. An accurate weighing 

 of their relative importance may perhaps do much to explain the earth's climatic history. 



The conclusion just stated seems to carry with it the assumption that there is some 

 relation between deformation of the earth's crust and periods of instability and variable 

 radiation in the sun. Such an assumption leads at once to the inquiry whether any possible 

 cause can be assigned for coincident or related activities of the two bodies. It is easy 

 to speculate as to hypothetical changes in the relation of the solar system to the rest 

 of the universe, as to possible magnetic variations, or as to the passage of the solar system 

 through portions of space characterized by conditions different from those in which it 

 now finds itself, but such speculation is fruitless. Another line of inquiry relates to the 

 possible passage of our system through swarms of meteorites so large and numerous 

 that their collisions with the various members of the solar system would produce appre- 

 ciable effects, but here again we have not the slightest basis for theorizing. It is perhaps 

 more probable that the gravitative or magnetic forces of the sun itself cause that body alter- 

 nately to fall into periods of quiescence or activity. This activity may be communicated 

 to the earth in some such way as that in which the magnetic changes of the sun are known 

 to produce an immediate terrestrial effect. Other lines of thought might also be suggested, 

 but even to mention them would scarcely be worth while. All that we can say is that, in 

 spite of the absence of any assignable cause, there seems to be some ground for the hypothe- 

 sis that throughout the course of geological history disturbances of the earth and of the 

 sun have occurred at about the same time. According to our present hypothesis, dis- 

 turbances of the earth seem to have caused deformation of the crust, accompanied often- 

 times by volcanic outbursts, and causing a redistribution of climatic zones in accordance 

 with the new outUnes of continents and the new courses of winds and currents. Those of 

 the sun, on the other hand, seem to have caused that body to throb with pulsations of 

 various lengths whose greatest effects are seen in glacial and interglacial epochs, while the 

 minor effects appear in little cycles like those whose a\'erage lengths now appear to be 

 about 11 and 35 years. Because of the earth's small size or rigidity, its activity appears 

 to have come to an end more quickly than that of the sun, as appears from the fact that 

 in general the upheaval of continents and mountain systems has preceded the periods of 

 most marked climatic instabihty. 



Beyond this it would at present be useless to attempt to go. Our suggestion of a possible 

 relation between the internal activities of the earth and the sun is merely one among several 

 working hypotheses. It seems to be the logical conclusion of our study of terraces, 

 lacustrine strands, ruins, the growth of trees, the rise and fall of civilizations, and the 

 occurrence of glacial periods in geological times. Yet its truth or falsity has nothing to 

 do with the verity of our hypotheses as to these other matters. It may prove wholly 

 wrong, but that does not in the least affect them. In the same way some other hypotheses, 

 such as our inferences as to the relation of pre-Columbian civilization to changes of climate, 

 may also prove to be insufficiently grounded and may have to be much modified, but this 



