174 The Petrography and Genesis of Sediments 



the two Monmouth samples 11 and 12 is not so clear, but it is perfectly 

 reasonable that sample 11 should be of the estuarine and sample 12 more 

 of the deeper-water type whether they are the product of different more 

 or less contemporaenous fades, or of successive stages in a transgression. 

 There is a general feature which was not taken up in the discussion 

 of the individual samples because the facts were not sufficiently signifi- 

 cant. This is the mineral content of the beds. It was thought that some 

 light might be thrown on the source of the material by the rarer minerals : 

 but their most striking characteristics are their similarity in different 

 beds and their apparently nearby origin. Moreover, their resemblances are 

 not only with each other but extend far beyond to such sedimentary beds 

 in general as have been studied from this point of view. Many of the 

 same minerals will be found to prevail, for instance, in the materials 

 studied by Cayeux and Thoulet, 1 or in other such studies as listed by 

 Andree. 2 Even common experience teaches the prevalence of magnetite 

 in stream-borne sands: and epidote while less easily recognized is prob- 

 ably almost as common, is in fact said by Van Hise 3 to be one of the 

 characteristic minerals of sedimentary rocks. Equally, or even more 

 frequent are chlorite and muscovite. Tourmaline, rutile, and zircon 

 survive in almost all sediments if there is any source for them. The per- 

 sistence of enstatite in these samples is apparently a more local char- 

 acter but can be accounted for by the occurrence of the mineral in the 

 rocks of the neighboring Piedmont region. It tends to bring out, how- 

 ever, the predominance of minerals that might at least be of nearby origin, 

 in these sediments. It is this fact which obscures other evidence and makes 

 it possible to say only that the Piedmont region appears to be the source 

 of most of this material. But in this connection two important facts 

 should be noted. One is that the Piedmont region is petrographically so 



1 Cayeux, Lucien, Contribution a l'etude micrographique des terrains sedi- 



mentaires. Mem. de la Soc. Geol. du Nord., T. iv-2. Thoulet, J., Etude 



bathylithologique des cotes du Golfe du Lion. Annales. de l'lnst. Oceanograph. 

 T. iv, Pasc. 6, Paris, 1912. 



'Andree, K., Sedimentbildung am Meeresboden. Geol. Rundschau, vol. 3, 

 1912, pp. 324-338. 



3 Van Hise, C. R., A treatise on metamorphism. Mon. IT. S. Geol. Survey, 

 No. 47, 1904. 



