264 University of California. [Vol. 2. 



coastal flats, and which correspond to the alluvial plains of 

 Modern age along nearly all our rivers in the United States. 



Modern Stream Gravels. — -Along many of the streams of the 

 Isthmus there are beds of large boulders, coarse gravel and sand, 

 which form terraces or elevated alluvial plains, not nearly as high 

 as the ancient river gravels on the Aguadulce-Santiago plain, but 

 still for the most part out of the reach of the present streams. 

 They are the gold-bearing gravels. They seem to indicate a slight 

 uplift of the land in a time very recent. It is this elevation of the 

 interior which I correlate in a general way with the recent sub- 

 sidence of the coastal regions and consider both to have occurred 

 at about the opening of the Modern or present epoch of the 

 Pleistocene era. 



SUMMARY OF POST-EOCENE EARTH MOVEMENTS. 



The disturbances of the level of the land on the Isthmus of 

 Panama, since the Eocene period, may be summarized as follows: 



1. A marked elevation supposably at about the middle of the 

 Miocene period. 



[a] A long quiescent period resulting in the formation of the 

 Tertiary peneplain. 



2. Another marked uplift, inferentially in some part of the 

 Pliocene period. 



(l>) Erosion of deep valleys in the mountains and formation of 

 Pleistocene peneplain. 



3. An uplift near the middle of the Pleistocene period. Insig- 

 nificant in amount on coasts as compared with previous uplifts. 



(r) Excavation of canon valleys in uplifted coastal plains and 

 deepening of cordilleran valleys. 



4. An extended but slight submergence of coastal lands near 

 the opening of the Modern epoch, with probable correlative 

 elevation inland. 



(d) Formation of low coastal plains on the Pacific side and 

 coral reefs on the Caribbean side of the Isthmus, as at Colon. 



