176 The Petrography and Genesis of Sediments 



samples. While the coexistence of solution and deposition of the same 

 substance in a bed seems at first inconsistent it may nevertheless be 

 in conformity with the recognized principle of chemistry that among 

 particles of substance in a medium in which they are partly soluble the 

 larger particles will tend to grow at the expense of the smaller. Or the 

 nuclei around which deposition took place may have been in some way 

 chemically different. Whether these supposed secondary grains have 

 definite nuclei and what these nuclei are was not determined, though thin 

 sections might throw some light on the question. The peculiar complete- 

 ness in the form of these grains was noted and seems to be the fact most 

 inconsistent with the hypothesis of their secondary origin. That strong 

 chemical action is indicated by the abundant deposition of sulphide in the 

 bed should be borne in mind in this connection. 



To conclude the general summary it may be said that in all the samples, 

 no matter what the form of the coarser sizes of sand, there is never any 

 appreciable amount of rounding below the fine-sand size (i. e., -J- mm. to 

 \ mm.). 



THE 6LADC0NITE 



Collet's * little manual on marine sediments contains so complete and 

 up-to-date a summary by a specialist on glauconite, contributing even 

 some hitherto unpublished data, that it is unnecessary to enter into a 

 general discussion. 



But perhaps by way of preface, since others may, like the writer, have 

 considered glauconite a comparatively rare mineral, it will be worth 

 while to draw attention to its distribution in marine sediments. So 

 common is it, indeed, that Collet considers it necessary to explain its 

 absence rather than its presence. 2 It is found more or less along the 

 coast of all the oceans at depths varying from 91 m. along the northern 

 Atlantic coast of the United States to 3512 m. in the Indian Ocean. In 

 the red clays which cover the greater depths, it is, for some undetermined 

 reason, absent. 



1 Collet, L. W., Les depots marins, pp. 132-194, 303-306. Paris: Octave Doin, 

 1908. 



2 Collet, pp. 303-306, addenda on the red clays. 



