INDUSTRIAL PROGRESS DURING THE YEAR 1875. cxiii 



with and penetrated by serpentine, and is accompanied by 

 hornblende, enstatite, and chlorite. Veins and fissures cutting 

 these ore-bearing strata are filled with a great variety of 

 crystalline minerals, including those already named and 

 many more. Among these is a mosaic of dolomite and ser- 

 pentine, both in cubic forms, copied from some undetermined 

 species. These imitated forms are at first described by 

 Dana as pseudomorphous from alteration, but subsequently 

 in the same paper as results of " substitution, and not of al- 

 teration;" the latter view being doubtless the correct one, 

 though the precise mode of their formation is still obscure. 

 Besides these, the vein-stones present a great variety of other 

 interesting examples of substitution or replacement of con- 

 temporaneous crystallization and envelopment, which are 

 often vaguely included under the name of pseudomorphs. 

 The phenomena to be observed in vein-stones, where minerals 

 have been successively formed in fissures which have been 

 through long periods channels for the circulation of watery 

 solutions of varying composition, alternately depositing crys- 

 tals, incrusting them, dissolving them, and again depositing 

 others, are exceedingly complicated; but it should be remem- 

 bered that these various reactions are from the nature of 

 things inapplicable to the solid masses of previously formed 

 rocks. 



The examinations of the deposits from deep-sea soundings 

 have much geological interest. It appears from the obser- 

 vations made on board the Challenger that the deposit over 

 great areas is a nearly pure calcareous ooze, chiefly made up 

 of the shells of globigerina. Below 2000 fathoms, however, 

 the calcareous matter diminishes in amount, and at 2600 

 fathoms disappears, a fine red clay, with silicious tests of dia- 

 toms and radiolarians, taking its place; while at still greater 

 depths the proportion of clay diminishes, until at length the 

 ooze consists chiefly of the remains of these silicious organ- 

 isms, which are probably more abundant at great depths, 

 while the foraminifera belong to shallower waters. The ab- 

 sence alike of these organisms and of their remains in deep 

 waters is ascribed to the solvent action of the waters, aug- 

 mented by pressure, and holding in solution carbonic acid, 

 and the red clay is regarded as the insoluble residue from 

 the globigerina ooze. It is described as a silicate of alumina 



