226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



determinate evidence that a molten condition was preponderant 

 even in the interior. The interior conditions of the earliest as well 

 as the later stages are to be reached only by indirect rather than 

 immediate inference. Under the influence of inherited presump- 

 tions, it may seem to many still probable that the interior of the 

 mature earth was once dominated by a molten condition at some 

 remote stage, but the evidence of powerful inthrusting of the igneous 

 element into even the earliest terranes, so often shown in the oldest 

 intrusions, seems to imply that the molten element was ever in the 

 strong grasp of stresses of the type normal to a rigid globe. This 

 harmonizes with the belief that the liquid matter was then only a 

 minor and passive factor, not a controlling one. 



If the earth were once wholly molten, the material for all the 

 stratified rocks of later ages must have been derived from the primi- 

 tive crus-t after it was formed and forced into positions of erosion, 

 or else from matter extruded through it. This primitive feeding 

 ground should, it would seem, be a notable feature on the geological 

 map. The absence, according to present knowledge, of any great area 

 of rocks bearing the distinctive characteristics of the supposed con- 

 gealed surface greatly weakens the assumption that the postulated 

 molten state ever obtained, at least in the mature earth. 



A study of the stress conditions of the interior of the earth seems 

 to call for a similar reversal of the inferences once drawn from the 

 igneous rocks. From the earliest well-recorded ages, the exterior of 

 the earth has given evidence of broad topographic reliefs taking the 

 form of great embossm.ents and broad basins. These surface con- 

 figurations must have conditioned the localization of extrusions and 

 the deployment of the effusive material. If the lavas arose from a 

 general and abundant source of supply which was responsive to gen- 

 eral and poAverful stresses, vestiges of these conditions should be 

 found in vast volumes and broad deployments of the lava floods. 

 If, on the other hand, the molten material formed but a fraction of 

 the whole mass, and was variously distributed through it, the result 

 should be a multitude of driblets squeezed out here and there in such 

 special situations as the controlling stresses required, or else a multi- 

 tude of limited intrusions forced into weak portions of the earth 

 body where the stresses were less imperative. The latter rather than 

 the former seems to accord with the testimony of the record. 



Now there is abundant geological evidence that the earth body 

 has been subjected at repeated intervals to strong compressive 

 stresses, by which its outer portion has been folded into mountainous 

 ranges or pushed up into great plateaus, while masses of con- 

 tinental dimensions have been raised, relatively, to notable heights, 

 and the bottoms of basins and deeps have sunk reciprocally to even 

 greater relative depths. The internal stresses which these deforma- 



