50 PROCEEDINGS OF WASHINGTON MEETING. 



Besides the pyrite at the top of the glauconite bed, the same mineral is often 

 found in greater or less quantity lower down in the formation, and where it has 

 been oxidized it gives rise to masses and layers of hydrous sesquioxide. Carbonate 

 of iron in the form of layers or nodules or as a finely disseminated material is also 

 a common constituent not only of the special glauconitic formation in question) 

 but also of many other Tertiary glauconites of the Gulf basin, and by its oxidation 

 also gives rise to the hydrous sesquioxide. The ferruginous solutions derived from 

 the pyrite or carbonate often percolate through the glauconite bed and deposit thin 

 layers of brown hematite in joint cracks and along lines of 1 tedding, often giving 

 the impression that the ore has been derived from the oxidation of the glauconite. 

 In some cases the glauconite has undoubtedly supplied a part of it, but the fact 

 that the largest quantities of the sesquioxide are found in those parts of the glauco- 

 nite beds which contain most carbonate or sulphide of iron is strongly suggestive 

 of the greater influence of the last two as sources of the sesquioxide. The long- 

 continued action of sulphuric acid derived from the oxidation of pyrite, and of 

 carbonic acid derived from carbonate of iron, however, have had their effect in 

 decomposing the glauconite, and their influence is shown by the fact that where 

 oxidation has gone on in the pyrite and carbonate the originally green glauconite 

 is converted to a yellow or rusty, more or less indurated mass. Sometimes it is 

 hardened to such an extent as to be used for building stone. A similar alteration 

 of the glauconite takes place even where the sulphide and carbonate are absent, but- 

 less rapidly than where they are present. In fact, in the region of the ores asso- 

 ciated with glauconite in eastern Texas the whole formation presents a yellow or 

 brown surface exposure, while at depths of from a few inches to twenty feet or 

 more in the interiors of the hills the original green color is preserved. 



( Inclusions. 



From the above discussion the following general conclusions have been 

 reached: 



1. That the iron ores of Texas and Arkansas occur mostly in two positions in the 

 Eocene series of the Tertiary. 



2. That the ores were originally deposited in the form of oxide, carbonate and 

 sulphide contemporaneously with the associated strata, and that they were sub- 

 sequently segregated mostly as carbonate and sulphide. 



3. That the ores as now found are the products of the oxidation of the carbonate 

 and sulphide, the nodular ores being derived from the carbonate and the laminated 

 ores from the sulphide of iron. 



Professor I. ('. White was called upon to take the chair, and the fol- 

 lowing paper was read : 



SANDSTONE DIKES IX NORTHWESTERN NEBRASKA. 



BY ROBERT HAY. 



At the meeting of the American Association for the Advancement of Science at 

 Ann Arbor in 1885, Professor A. E. Crandall read a paper on " The occurrence of 

 trap rock in eastern Kentucky," away from all centers of eruption. In the ensuing 

 discussion, Professor L. E. flicks, of Nebraska, mentioned a dike near Chadron, in 



