220 SEE— FURTHER RESEARCHES ON [Apnl 24, 



crust was pushed hither and thither by earthquakes, raising ridges 

 and undermining the troughs, till the rocks were crumpled and 

 folded as we find them to-day. The simplicity of tJiis cause, and the 

 easy zvay in zvhich zve pass from tJie living troughs now being dug 

 out in the sea to fossil troughs long since dead and now far inland 

 give a genuine palcontological interest to the science of mountain 

 formation. What has long been mysterious and nearly inexplicable 

 is now as clear as any theorem in geometry. 



§ 30. Application of the Nezv Theory to the Allegheny Moun- 

 tains. — The Allegheny Mountains in Pennsylvania and Virginia are 

 very remarkable for the great extent of the folds, and it seems 

 worth while to dwell a moment on the mode by which these folds 

 were produced. We have seen that they all arose in the sea, and by 

 a repetition of the earthquake process of digging out trenches along 

 the ancient shore line. As we shall see in Part V, § 41 of this paper, 

 Professor James Hall so long ago as 1857 announced to the Ameri- 

 can Association in session in Montreal that the enormous thickness 

 of the formations along the Appalachian Chain in the United States 

 was due to the prolonged accumulation of sediments over a sinking 

 sea bottom, at the niargin of the continent, where the marine cur- 

 rents allowed the material to deposit. 



Obviously if sea trenches were dug out by earthquakes they 

 would become the basins for the accumulation of a vast amount of 

 detritus. And when several trenches were successively dug out in 

 the sea bottom by earthquakes depending on the Atlantic, would not 

 the resulting folds give us the Allegheny, Tuscarora and Blue Ridge 

 Mountains of Pennsylvania and Virginia? The famous Shenandoah 

 Valley in Virginia is nothing but an ancient sea trough ; and Penn- 

 sylvania has many such valleys originally formed in the depths of 

 the sea. This is clearly indicated by the beautiful parallelism of the 

 mountain ranges. 



It is noticeable that the sea trench south of the xA.leutian Islands 

 is remarkably straight, and one may easily predict that the ranges 

 hereafter to be formed in the North Pacific Ocean will be remark- 

 ably parallel like those now seen in Virginia and Pennsylvania. 

 Under the circumstances can any one doubt that the sea was once 

 very deep near where the Blue Ridge stands to-day? 



