6 PROCEEDINGS OF THE NATIONAL. MUSEUM vol.72 



absence of this constituent in the latter. If we interpret Tassin's 

 results in mineralogic terms, the following results are obtained : 



1. 2. 



Limonite (2Fe203.3HoO) 69.27 88.73 



Magnetite (FeO.FosOs) 2.69 None. 



Trevorite (NiO.Fe.O3) 27.53 14.50 



Cobalt trevorite (CoO.Fe^Oa) 1.26 



Sclireibersite (Fe^NiP) 1.80 .58 



There is no excess of FeoOg in the above interpretation. In fact 

 there is not quite enough shown by either analysis to use up all of 

 the water as a limonite with the formula above used for this mineral. 

 Limonite is an amorphous material having the composition 

 Fe203.H20, usually with approximately the additional amount of 

 water necessary to approximate the formula above used. This min- 

 eralogic interpretation is of interest in comparison with Tassin's 

 discussion of his results. He disagrees thoroughly with Farrington's 

 interpretation and regards the shale as made up essentially of 

 limonite and some turgite, saying that this opinion is based upon 

 the physical characters of the shale in preference to data derived 

 by the arbitrary combining of the bivalent bases to form ferrites. 

 Tassin says positively that, in the portions analyzed by him, the 

 magnetic character of the samples was certainly due to the relatively 

 large amount of unaltered sclireibersite present and which was 

 plainly visible in many sections of the iron shale. The inconsistency 

 of this reasoning is patent from his analytical figures. His results 

 for phosphorus are equivalent to only 1.30 per cent of sclireibersite 

 in the first sample and 0.58 per cent in the second. To these small 

 amounts certainly can not be credited the strong magnetism of the 

 samples. 



The specimen supplied for examination to the writer by Doctor 

 Merrill is a nodule of blackish-brown color and brecciated appear- 

 ance. Its main mass is composed of hard lustrous brownish to blue- 

 black homogeneous-appearing material of submetallic luster. The 

 cracks and interstices are filled with a little yellow ocher and pink- 

 ish material of clayey appearance which contains some carbonate. 

 When crushed to pass 80 mesh the powder is near Mars brown, 

 Ridgway (13'm) and is entirely picked up with an ordinary horse- 

 shoe hand magnet. The material is not polarized. Fairly large 

 chunks of the unground material are easily lifted by the magnet. 

 The partial analysis was made by the following procedure. One-half 

 gram of the sample was dissolved in boiling 1 : 3 sulphuric acid in 

 an iron reduction flask through which a current of COo was passed. 

 After titration for ferrous iron, the whole solution was reduced by 

 hydrogen sulphide, the hydrogen sulphide expelled with carbon di- 



