1898.] PECKHAM — THE GENESIS OF BITUMENS. 109 



nomena of rock building. Mineral silicates were then supposed 

 to have crystallized from igneous fusion, and the deposition of sedi- 

 ments to have resulted only in amorphous, uncrystallized rocks. 

 The idea that heat and water together may have produced all of the 

 phenomena that have been attributed to the action of either alone 

 has been of slow growth ', but may now be said to be pretty 

 generally accepted, although there are those who refer to the 

 action of heat and of pressure alone phenomena that are without 

 doubt properly the resultant of the action of heat and steam under 

 pressure. 



3. The discussions that have proceeded along the three lines of 

 geology, chemistry and mineralogy, have been mainly directed to 

 an elucidation of the problems relating to the formation of the 

 crystalline rocks. To determine, therefore, the nature of metamor- 

 phic action and the conditions under which it might take place, was 

 the problem to the solution of which Bischof, Hunt, Delesse, 

 Daubree and several others of the most gifted chemical geologists of 

 this century devoted themselves.^ These gentlemen first considered 

 the reactions that according to known chemical laws must follow 

 the cooling of a heterogeneous mixture of the elements composing 

 the earth, in a state of gaseous fluidity, and at a temperature that 

 rendered chemical combination impossible ; in other words, a state 

 of complete dissociation. It follows that the most infusible ele- 

 ments would first condense and form a solid nucleus around which 

 would float an ocean, in a state of igneous fusion, of more fusible 

 elements and compounds, while over all would hover an atmosphere 

 containing all the nitrogen and oxygen, the free hydrogen, sulphur 

 and allied elements, with the chlorine and other halogens. As the 

 cooling proceeded the silicon would combine with oxygen and 

 bases, forming both acid and basic silicates, which would constitute 

 a solid crust. The hydrogen and haloids combining would form 

 the haloid acids and the sulphur and allied elements would form 

 oxygen acids, all the hydrogen being oxidized into water, which 

 with the acids would be alternately condensed and evaporated, fall- 

 ing as an acid rain upon the surface of silicated rocks, which in turn 



1 G. Bischof, C/iem. and Phys. Geology, Cav. Soc. ed. T. S. Hunt, Chein. 

 and Geolog. Essays. Delesse, " Essay on Pseudomorphs," Ann. des Mines, 

 xii, 509 ; xiii, 393, 415 ; xvi, 317-392. Mem. Acad, de Scien. de France, xvii. 

 Daubree, Cofupies Kendtis de VAcad., November 16, 1857. Etudes et experi- 

 ences synthetique stir le Metamorphisme, Paris, 1859. 



