HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 105 



mals and their fragments, and no doubt had a much broken, open tex- 

 ture. If there was, as yet, no atmosphere or hydrosphere, as in the 

 case of the moon, there was no effective means for the washing of fine 

 fragments into the interstices of the coarse, or, what is more impor- 

 tant, for the solution of the material at the surface and the cementa- 

 tion of that below into a solid mass, as is the present habit on the earth; 

 in other words, there was no effective healing process to unite the broken 

 fragments. The porous clastic zone 

 must, therefore, have extended 

 downward to a depth at which 

 gravity was able to force the frag- 

 ments into continuity by its crush- 

 ing effects. In a small body this 

 zone would be deep. 



When the rising lava-tongues 

 reached this outer fragmental zone, 

 fluxing was no longer required, as 

 they could force their way by insinu- 

 ation and by mechanical displace- 

 ment. It appears almost certain 

 that, in the upper part of such a 



fragmental zone,the interstices would Fig. 32.— Ideal secMon of a portion of 

 make up a sufficient part of the vol- 

 ume of the aggregate mass to reduce 

 its average specific gravity to a fig- 

 ure below that of the penetrating 

 lava, even though the latter might 

 be made up of lighter material in- 

 herently, and was also hot and liquid. 

 The earliest tongues of molten 

 material are supposed, therefore, to 

 have generally lodged within the 

 fragmental zone, taking various plutonic forms, as dikes, sills, lacco- 

 liths, and batholiths, and to have there given off their gases, which, 

 more or less concentrated and condensed, doubtless not infrequently 

 forced an exit to the surface by blowing away the overhang fragmental 

 material (Fig. 32). The slight coherence of this material, the low 

 gravity of the young earth, and the absence or scantiness of a resisting 



the early earth, illustrating its as- 

 signed modes of vulcanism. C, cen- 

 ter; S, surface; a-a' ', fragmental 

 zone; a'-f, zone of continuous rock 

 below surface melting temperature; 

 ff-c, interior portion whose tempera- 

 tures rise from the surface melting- 

 point at /-/ to a maximum at C; V, V, 

 threads or tongues of molten rock 

 rising from the interior to various 

 levels, many of these lodging within 

 the fragmental zone as tongues, 

 batholiths, etc. ; PPP, explosion pits 

 formed by volcanic gases derived from 

 tongues of lava below. 



