156 ANNALS NEW YORK ACADEMY OF SCIENCES 



dish brown color, the transition taking place within a thickness of twa 

 inches or less, the texture and general appearance of the rock suffering 

 no alteration otherwise. The percentages of silica and total iron in two 

 specimens of the building stone, red and gray, from horizons twenty feet 

 apart in the Princeton quarries, are almost identical : 



Massive red argillite, SiOg, 46.40 per cent. Total iron, 6.05 per cent. 

 Massive gra}' argillite, SiOs, 46.42 per cent. Total iron, 5.61 per cent. 



A content of seven or eight per cent of total iron seems to be normal for 

 these rocks, and some such amount usualty appears in the analyses. Thus 

 it is with the following series of analyses : 



Determinations of Iron in Lockatong Argillites 



Sample FeO Fe,03 Total Fe 



Per cent Per cent Per cent 



1 3.57 7.80 8.28 



2 3.65 7.88 8.40 



3 1.16 9.38 7.50 



4 4.40 3.81 6.10 



5 7.15 4.52 8.77 



9.30 0.91 7.91 



7 5.12 4.97 7.50 



8 5.65 5.07 7.98 



Red Argillite Samples : 



1. McCarthy's Quarry. Princeton, bottom of quarry wall. 



2. McCarthy's Quarry, Prmceton, middle of quarry wall. 



3. McCarthy's Quarry. Princeton, top of quarry wall. 



Gray Argillite Samples : 



4. McCarthy's Quarry, Princeton, middle of quarry wall. 



5. McCarthy's Quarry. Princeton, top of quarry wall. 



6. Shanley's Quarry. Byram. Analysis by R. B. Gage. 



7. Scudders Falls, Traction Company's quarry, bottom of quarry wall. 



Olive Green Argillite : 



8. Scudders Falls, Traction Company's quarry. 



On each of the al)Ove. duplicate determinations closely agree. 



The percentage of Fe203 is in every case much higher in the red rocks 

 than in the gray ones. This indicates that the color of the red layers is 

 due to the presence of hematite, w^hile that of the gray layers is partly or 

 wholly due to fen^ous iron. This is in accordance with the work of 

 Spring, who obtained results of a similar nature from the study of red 

 and gray sediments of Devonian age. 



