The naturalist 



For 1890. 



CAUSE OF 

 THE COLORATION OF RED SANDSTONES. 



T. MELLARD READE, F.G.S., 

 Park Corner, Bluiuiellsands, Lh'erpool. 



While walking along the shore at Hightown my attention was 

 called by one of my sons to several small patches of red sand which 

 occurred among the ordinary light yellow sand of the sand-dunes. 



The face of the sandhills at this point is nearly vertical, having 

 been cut into by the sea. The patches in question were so unusual, 

 and looked so exceedingly like disintegrated Triassic sandstone 

 that we were all much interested. On digging out a portion of the red 

 sand at two places, we found that on the top of one of the patches 

 was a large iron nail, and on the other several small ones much 

 rusted. It is evident that the coloration was produced by the 

 oxidation of these nails, the remarkable fact being the uniformity of 

 tint given to the sand below and its redness. 



An examination with the microscope showed that the grains, like 

 those of our Triassic sandstones, were more or less coated with 

 a pellicle of peroxide of iron. Some were a light translucent pink, 

 others a darker pink, while a few of the grains appeared a very dark 

 brown, the general effect being a pinky red. 



I consider this an interesting illustration of how our red Triassic 

 Sandstones may in many cases owe their coloration to percolation of 

 water holding ferrous oxide in solution. It shows that a deposit of 

 peroxide of iron may in this way take place on the individual grains 

 in a tolerably uniform manner. 



Mr. Israel Russell has, in a very interesting and valuable 

 memoir, published by the U. S. Geological Survey (Bulletin, No. 52, 

 1889), given reasons for believing that the Red Rocks of the Newark 

 System, which includes the Trias, Jura, and Jura-Trias, are sediments 

 derived from the residual deposits left by the sub-aerial decay of 

 rocks containing hornblende, mica, chlorite, garnets, and pyrites, etc. 



The oxide of iron arising from the decomposition of these 

 minerals colours the residual deposits a deep red, and Mr. Russell 

 considers that the red rocks of the Newark System are these 

 deposits aqueously re-arranged. Nature does not, however, always 



Jan. 1890. A 



