52 Prof. J. D. Dana on some Results of 



under the designation of a polygenetic mass. Thus the Con- 

 necticut-valley sandstone beds, which must have been but little 

 raised by the slight upturning they underwent at the epoch of 

 their disturbance (since there was then neither plication nor 

 crushing), are now 700 feet higher above the sea-level in Mas- 

 sachusetts than near New Haven, Connecticut; and this is 

 owing, not to denudation, but to a subsequent elevation in which 

 much of New England participated — a true geanticlinal uplift. 

 So it has been the world over. The great uplift of the Rocky- 

 Mountain region of more than 8000 feet, which began after the 

 Cretaceous, had nothing to do, as I have said, with crushing or 

 plication, although there was disturbance of the beds in certain 

 local Cretaceous and Tertiary areas ; it appears to have been a 

 true geanticlinal elevation of the Rocky-Mountain mass, itself 

 mainly, if not wholly, a combination of synclinoria. 



Geosynclinals and geanticlinals of low angle, like those of the 

 present day, graduate insensibly into horizontal surfaces. The 

 later oscillations in the world's history have taken in a vastly 

 wider range of crust than those of early time. We cannot point 

 to any geosynclinal in progress that is probably on the way to 

 become the site of a new synclinorium. This comes from the 

 fact already stated, that the completion of a synclinorium has 

 generally consisted in the solidification as well as plication of 

 the rocks, and the addition of the whole mountain-region to the 

 more stable portion of the earth's crust ; and the further fact 

 that this process has been often repeated in past time, until the 

 crust has been so stiffened above, as well as below, that only 

 feeble flexures of vast span are possible, even if the lateral pres- 

 sure from contraction had not also declined in force. 



4. How was the lateral thrust from the direction of the ocean made 

 to differ in its action or results from that from the opposite di- 

 rection ? 



The fact of a difference in the effects of the lateral thrust from 

 the opposite directions, the oceanic and continental, is beyond 

 question. The evidence may here be repeated. 



The greatest of elevations, as well as subsidences, and also of 

 plications and igneous eruptions, have taken place on the conti- 

 nental borders or in their vicinity ; they thus show that there is 

 something peculiar along such regions. Again, the border 

 mountains in North America are parallel to the axes of the ad- 

 joining oceans, and thereby at right angles, instead of parallel, 

 to one another. Again, the folds in the Appalachians are not 

 symmetrical folds, but, instead, have one slope much steeper 

 than the other, proving inequality in the action of lateral pres- 

 sure from the continental and oceanic directions. Further, the 



