EARLIEST SEDIMENTARY ROCKS 249 



wholly derived from the primitive land areas by rock destruction. The 

 new hypothesis allows a different view. 



"According to this, the ocean began its work long before the earth and moon 

 had attained full size by gathering to themselves all the particles of the earth- 

 moon ring or zone. Consequently there were oceanic sediments which were not 

 wholly detrital, but were primitive world-stuff. The earlier ocean sediments 

 must have been deeply buried under the later, and may now constitute part of 

 the interior mass of the globe. It may be that the globe had attained full size 

 before any of the visible clastic rocks were made. With the water on the earth's 

 surface increasing by supplies from the interior and with matter still being gath- 

 ered in from the exterior, the depressions of the primitive continents were more 

 or less filled by a mixed class of sediments partly formed from clastic material, 

 partly from volcanic, and partly from the material of incoming planetesimals. 

 Encroachments of the ocean on the continents probably occurred as in later times, 

 followed by withdrawals as the ocean basins sank and increased their capacity, 

 As the decomposition of the clastic material was probably less complete than in 

 later times, from lack of vegetal covering and other causes, the mixed sediments 

 when metamorphosed resembled original igneous rock, and it is now difficult to 

 distinguish the metamorphosed elastics from true igneous rocks."* 



With the passing of the old hypothesis, it will be desirable to change 

 the terminology of the rocks as far as this now implies an original 

 molten or " igneous " state of the earth. Some new name will be desira- 

 ble for the sediments which were formed chiefly or wholly from the 

 planetesimals (the cosmic matter) in the early seas of the growing 

 globe. Let us call such deposits cosmoclaMics, and the primitive massive 

 rocks, the cosmics. The downward succession of the rocks would thus 

 be, from unaltered elastics through altered elastics (metamorphics) to 

 metamorphosed cosmoclastics ; while beneath these, perhaps ever invisi- 

 ble, lie the altered cosmics, the primitive deposits. 



The above theoretical succession of the strata, the slow upward grada- 

 tion from primitive world-stuff into the differentiated secondary sedi- 

 ments, seems in better accord with our knowledge of the deep-seated 

 rocks than the assumptions of the old hypothesis. 



Volcanic Phenomena 



The vast extrusions of molten rock over the earth's surface without 

 explosive phenomena, and the intrusions into the superficial zone known 

 as dikes, sills and laccoliths, may be in harmony with either hypothesis 

 of world genesis, as the main factors seem to be great internal heat, 

 potential fluidity, relief of pressure and hydrostatic equilibrium. How- 

 ever, under the old hypothesis, which favors homogeneity in the in- 



* Quoted from Le Conte's Elements of Geology, 5th edition, p. 299. 



