126 The Petrography and Genesis of Sediments 



SAMPLE NO. 2 (FIG. B, p. 169) 

 Serial number : 10. 

 Field number : 1M0-2-1911. 

 Formation : Magothy. 

 Locality : Better-ton. 



Appearance : A hard, blue-gray, faintly laminated clay in layers about 1 inch thick with 

 saDdy partings. 



Mechanical Analysis 

 Sample 14.050 gm. 



Per cent of 

 sample 



Sands 14.2 



Silt 13.2 



Clay 66.8 



Total 94.2 



Per cent of 

 total sands 



Coarse sand 0.7 



Medium sand 6.6 



Fine sand 6.3 



Very fine sand 43.9 



Extra fine sand 42.7 



Total 100.2 



Per cent of 

 fine sand 



Light 87.5 



Heavy 12.4 



Total 99.9 



DESCRIPTION OF PRODUCTS 



A. Under the Hand Lens 



The coarse portion is only carbonaceous matter ; the medium-grained contains, in 

 addition, small rounded pyrite nodules, grains and Hakes of argillaceous matter, but as 

 primary minerals only a few flakes of mica. The fine-grained contains more of the 

 clay grains, and mica more abundant and in greater variety, there being chlorite as well 

 as muscovite. 



B. Under the Microscope 



I. Very Fine Sand 

 (1) Light 



Quartz : feldspar = 85 : 15. 



Besides feldspar and quartz carbonaceous fragments and argillaceous grains as in the 

 coarser portions, are important constituents. These two constituents are, in fact, so 

 abundant that they interfered with the study of the quartz and feldspar. A portion was 

 therefore incinerated and with the aid of this incinerated portion the following facts 

 could be determined. 



The plant fragments appear in two forms, one black and opaque, the other brown, 

 translucent, and generally showing some organic structure. The incinerated portion 

 turned from black to red. Under the microscope it was then found that most of the 

 opaque black fragments had disappeared but. the brown translucent remained with all 

 their structure, having apparently only turned red. It ihay be that some of the trans- 

 lucent had also disappeared but the essential point is that many of them, at least, were 

 evidently permeated, or perhaps partly replaced, by some iron salt which on incineration 

 preserved the form of the original plant fragment. 



Here too the clay grains, found in the other portions as well, could be studied under 

 the microscope. The facts about them may therefore be summarized. They are round 



