62 FROM NEBULA TO NEBULA 



sor Joly, for instance (Radioactivity and Geology, p. 97), 

 quotes Dana approvingly as follows : 



A mountain range of the common type like that to which the 

 Appalachians belong is made out of the sedimentary formation of 

 a long preceding era ; beds that were laid down conformably, and 

 in succession, until they had reached the needed thickness; beds 

 spreading over a region tens of thousands of square miles in area. 

 The region over which sedimentary formations were in progress 

 in order to make finally the Appalachian range reached from New 

 York to Alabama and had a breadth of 100 to 200 miles, and the 

 pile of horizontal beds along the middle was 40,000 feet in depth. 

 The pile from the Wahsatch Mountains was 60,000 feet thick, ac- 

 cording to King. The beds of the Appalachians were not laid 

 down in a deep ocean, but in shallow waters where a gradual 

 subsidence was in progress, and they at last, when ready for the 

 genesis, lay in a trough 40,000 feet deep, filling the trough to the 

 brim. It thus appears that epochs of mountain making have oc- 

 curred only after intervals of quiet in the history of a continent. 

 * * * Nor would the list of such crustal movements be complete 

 save in the enumeration of every great range upon the earth. 



Plainly, then, the formation of great mountain chains 

 is analogous to the action of condensed moisture on the 

 outside of an ice-cold pitcher. For a second or so, a small 

 drop, after coursing down an inch or two, will often stop 

 dead, held in its place by adhesion, until, being reinforced 

 by a fresh drop following in its track, it will again start 

 downward, perhaps to stop a second time and repeat the 

 performance before attaining the bottom. So, before a 

 mountain range can be lifted into place, a great dynami- 

 cal agency must be accumulated for the work in hand. 

 This Nature does gradually by laying one stratum upon 

 the other on the bed of the ocean and incidentally eroding 

 away the obstructing land in front out of which to form 

 those strata, until the weaker becomes the stronger, or the 

 lighter the heavier, and crowds its way onward toward 

 the "bottom". Of course this process is exceedingly 

 slow, and its results are normally very gradual, the strata 

 bending rather than fracturing ; but by no means is this 

 always the case, for sudden slips are here just as bound to 

 occur as landslips at the Panama Canal or iceslips in the 

 Alpine glaciers. I should like very much to pursue this 

 principle further into its many geographical, geological 



