938 HISTORICAL GEOLOGY. 



which is like the last in its rocks. Icldings refers these cones to the early- 

 Tertiary. He states that after a long period of eruption of acidic andesytes, 

 basic andesytes and basalts were ejected ; and after these had been much 

 denuded, the great outflow of rhyolyte took place, forming the Park plateau ; 

 and that finally the basalt was poured forth that extends widely over the 

 Snake River plains in Idaho. 



Igneous eruptions occurred through all the successive geological ages. 

 But at no time in American history since the Archaean, have they approached 

 in extent those of the Later Cretaceous and Tertiary periods. It was a time 

 of pouring from fissures and of the birth of volcanoes, as never before. 



It is not yet certain that a volcano ever existed on tlie continent of Nortli America 

 ■before tlie Cretaceous period ; for tlie published facts relating to supposed or alleged 

 volcanic eri;ptions in tlie course of the Paleozoic ages are as well explained on the suppo- 

 sition of outflows from fissures and tufa ejections under submarine conditions ; and none 

 of the accounts present evidence of the former existence of a volcanic cone, that is, of 

 an elevation pericentric in structure made by igneous ejections. Such cones in the 

 tropical Pacific are now encircled by coral reefs as well as beds of detritus, and are thus 

 In process of burial ; and so they might have been buried by limestone and other strata, if 

 an actual fact in Paleozoic North America. 



During the Archaean, to its end, igneous ejections were on a vast scale. Even after 

 the cooling had so far advanced that the sedimentary series in progress of deposition 

 attained a thickness of many thousands of feet before a crisis of upturning and meta- 

 morphism occurred, the heat from below, which was added to the heat of a dynamical 

 source to produce the metamorphism, was so far the greater of the two that fusion of the 

 lower beds would have generally taken place ; and, as a consequence, great effusions of 

 the melted rock through the overlying and much broken metamorphic beds, should have 

 occurred in true bathylithic style, as the facts attest. But there is no evidence that they 

 ever made Archaean volcanic cones. Archsean conditions gradually declined as Paleozoic 

 time was passing, and so also did the power of making bathyliths. Later came the 

 power, not merely of eruption through fissures, which has always existed, but also that 

 of producing lofty volcanic cones. 



• The volcanoes also of the Andes are supposed to be chiefly of Tertiary 

 origin. In Europe " the grandest volcanic phenomena were those of Oligo- 

 cene (Lower Miocene) times, to this date belonging the basalts of Antrim, 

 Mull, Skye, the Faroe Islands, and the older series of volcanic rocks in 

 Ireland" (Geikie). The volcanic eruptions of Auvergne, the Eifel, and of 

 Italy, Bohemia, and Hungary are referred mostly to the Tertiary. Asia, if 

 the ranges of islands off its eastern and southern coasts are excluded, is 

 peculiarly free from volcanoes. But the outflow of the Deccan trap in 

 peninsular India, 200,000 square miles in area, was an event of the early 

 Tertiary, and has been supposed to have occurred when the rising of the 

 Himalayas began. 



The concurrence during the era from the Later Cretaceous to the close of 

 the Tertiary of the most extensive orogenic work in the world's history, of 

 the chief part of its continental elevation, and unprecedented igneous erup- 

 tions, came when the earth's crust had reached a cooled condition that took 

 all past time up to the present era for its production. The inquiry thence 



