140 Scientific Intelligence. 



( Peace Creek (Florida). 



Pliocene < Blanco. 



( Paloduro (and Archer of Florida). 



, T „ , ( Loup Fork proper. 



( Loup iOYK -no- 



Miocene \ ' Dee P Rlver - 



I t | ^ ( Mesoreodon Beds (Montana). 



' y | Eporeodon Beds (Oregon). 



( Protoceras Beds. 



Oligocene. White River -^ Oreodon Beds. 



( Titanotherium Beds. 



George H. Williams, in his paper entitled, Volcanic Hocks 

 in the ancient crystalline belt of Eastern North America, called 

 attention to the widespread occurrence of truly volcanic rocks in 

 the paleozoic and pre-paleozoic formations of eastern North 

 America. He was led to a search for such rocks by the dis- 

 covery of their extensive development in the Blue Ridge between 

 Harrisburg, Pa., and the Potomac River, as described in this 

 Journal, Dec, 1892. Since that time personal observation has 

 disclosed great masses of similar rocks on the coast of Maine 

 and in the Carolinas, while the published literature renders prob- 

 able their abundant occurrence as far north as Newfoundland. 



After a review of the opinions prevailing in Europe as to the 

 nature of the differences between ancient and modern volcanic 

 rocks, the author enumerated the criteria necessary for the cer- 

 tain identification of ancient volcanic rocks. While regarding 

 the differences between the products of ancient and modern vol- 

 canoes as secondary and therefore non-essential, he considered the 

 proofs that any rocks called volcanic (in contrast to plutonic) 

 solidified at or very near the atmospheric surface as very impor- 

 tant. A tendency on the part of some geologists to use the 

 word volcanic, as synonymous with igneous is greatly to be de- 

 precated as introducing only confusion. The former term should 

 be employed, at least in the case of ancient rocks where the ex- 

 ternal form of the volcano has been destroyed, only for igneous 

 masses whose surface origin is beyond doubt. The most reliable 

 proofs are in the case of acid rocks glassy structures, which in 

 spite of complete devitrification will be preserved, and in the 

 case of basic rock an amygdaloidal or scoriaceous texture. Such 

 structures, while they may rarely occur in narrow dykes which 

 have very rapidly cooled, are essentially characteristic of lava 

 flows, especially if the rocks which exhibit them are of great 

 extent. But even better than these structures as proof of vol- 

 canic origin are accumulations of fragmental (pyroclastic) mate- 

 rial, tuffs, breccias, agglomerates, etc., stratified either by grav- 

 ity or water, which accompany such massive effusive rocks. 

 All of these proofs are abundant in the rocks to which the author 

 applies the designation volcanic. 



The distribution of ancient volcanic products was traced, either 

 by published accounts or by personal examination of material sent 



