HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 117 



it. It is, therefore, inferred that vulcanism continued to increase in 

 activity long after growth had entered on its decline, and that there 

 was an important period in which the dominant activity was volcanic. 



The ratio of the volcanic products to the accessions and to the deriv- 

 atives. — It is conceived that in the late stages of the earth's growth 

 the amount of material poured out on the surface in molten form, or 

 introduced into the outer parts of the earth from below, was very much 

 greater than the accessions from without. Still later these declining 

 accessions were so overwhelmed by the igneous extrusions that they 

 became indistinguishable contributions. In this stage, too, it is held 

 that the modifications wrought by the atmosphere, the hydrosphere, 

 and organic life were also quite subordinate to the volcanic contribu- 

 tions. Disintegration is assumed to have gone little farther, usually, 

 than to partially reduce rocks of the granitoid type to arkoses, and 

 those of the basic type to wackes. Rather rarely, it is believed, was 

 much pure quart zose sand, aluminous clay, or similar well-decom- 

 posed residuary material accumulated ; rarely, also, much carbonaceous 

 shale. Arkoses and wackes, when metamorphosed later, took on such 

 a similitude to igneous rocks as to be more or less unidentifiable. 



The Archean complex. — The formations of this period of volcanic 

 dominance, with very subordinate clastic accompaniment, are regarded 

 as constituting the Archean complex, though perhaps only the later por- 

 tions of the great volcanic series are represented by the known Archean. 

 Here, for the first time, we reach formations exposed to view, and 

 observational geology begins to replace the hypothetical. As inter- 

 preted in the light of the recent studies in both the Old World and the 

 New, the lowest accessible formations that can be given a place in 

 the systematic series were originally surface lava-flows, attended by 

 volcanic elastics in abundance, and by sedimentary elastics and chemical 

 and organic deposits in quite subordinate quantity. Into these were 

 intruded contemporaneously, and also at later stages of the same 

 great era, enormous embossments of granite and other rocks. This 

 intricate combination of surface flows, elastics, and intrusions, distorted, 

 sheared, and metamorphosed, makes up the vast Archean complex. 



Diastrophism accompanying the volcanic climax. — For obvious 

 reasons the great climacteric era of vulcanism was attended by defor- 

 mations of exceptional intensity. The transfer of so much material 

 from below to the surface required a readjustment, while the intrusion 



