cxiv GENERAL SUMMARY OF SCIENTIFIC AND 



and iron-oxyd, and is supposed, to be related to the coloring 

 matter of the red chalk of England, which is a silicate in which 

 the iron often greatly predominates over the alumina, and, as 

 Church has suggested, is probably a partially decomposed 

 greensand, or glauconite, which in various parts of the sea- 

 bottom is found, as in older formations, filling the cells of fora- 

 minifera, or appearing as casts of these from which the calca- 

 reous shells have been removed. The red soil which overlies 

 the white coral-sand of Bermuda is in like manner a silicate 

 containing more iron-oxyd than alumina, and is very unlike 

 a true clay in composition. Whatever may have been the 

 agencies by which the silica, iron, and alumina have been 

 brought together to form the glauconite which after the 

 death of the foraminifer replaces its sarcode, there is no 

 apparent basis for the notion of the organic origin of clays, 

 which has been suggested in this connection. The red clays 

 from great depths contain more or less oxyd of manganese, 

 which sometimes forms concretionary masses several inches 

 in diametef, or coats with a mammillated layer pebbles and 

 bits of pumice-stone in the red ooze. It has been suggested 

 that this may have been accumulated through the agency of 

 alga?, the ashes of some of which contain as much as four 

 hundredths of manganese. The oceanic circulation, which, 

 by carrying to the depths of the sea cold and aerated wa- 

 ters, makes possible these varied conditions of deposition, 

 is, as Carpenter has shown, excluded from basins which, like 

 the Mediterranean Sea, are cut off by submerged barriers 

 from the flow of the polar waters ; and hence the deposits 

 at comparatively moderate depths are there almost destitute 

 of organic remains. The bearing of all these facts upon the 

 rock-formations of past ages is obvious. 



GEOGRAPHY. 



The progress in Geography during 1875 has not been 

 marked by any very striking discovery, although a reasona- 

 ble average in the way of the extension of our knowledge 

 has been maintained. 



The following may be considered as among the more im- 

 portant points in the history of the year : 



Geodesy, Navigation, and Hydrography. An International 

 Geodetical Congress was held on the 20th of September in 



