1892.] Mineralogy and Petrography. 53 



stones from near Seaton, England, north of Neweastle-on-Tyne. The 

 harder shale layers arc composed mainly of mica, quartz, feldspar, 

 zircon and other accessory minerals, as garnet, rutile, anataso, tourma- 

 line, sphene and barite. The biotite is the first of these to iiiideriro 

 change under the influence of weathering processes. In the case studied 

 it has not changed to chlorite, but has become bleached and has yielded 

 epidote. The quartz and feldspar are uniformly distributed throughout 

 the mass, while the mica usually lies out its fiat surfaces in the bedding 

 planes. In addition to the mineral grains already mentioned there i> 

 present a sort of groundmass or paste, made up of indistinctly granular 

 matter, with microlites of various kind- and a hugv amount of a fine 

 micaceous substance, besides large plates of a secondary mica. In a 

 fine grained portion of the deposit, the paste is qiute abundant and in 

 it are numbers of minute rutile needles, flakes of ilmenite, some small 

 perfect crystals of tourmaline and a considerable quantity of the secon- 



edges of the grains extend out between the surrounding minerals, and 

 the plates are full of minute rutile needles. In the very finest grained, 

 smoothest clay bands of the region, the paste forms the largest part of 

 the mass, while the well marked clastic grains are few in number, the 

 biotite having disappeared entirely. Kaolin was not certainly recog- 

 nized in even the thinnest sections of fire-clay, the fine grained granular 

 substance of which this clay principally consisrs, being mainly the paste 

 described above. The abundance of rutile, that is so noticeable a feature 

 of the clays examined, is supposed to have originated upon the decom- 

 position of the biotites, and the muscovite (or sericite), by the alteration 

 of the paste. This mineral gradually increases in quantity, and then 

 under the influence of pressure is so orientated that a micaceous slate re- 

 sults. The absence of biotite from most slates is thought to be due to the 

 easy decomposability of the <ui>4ance; and its presence in the sediments 

 from which some slates were formed is thought to be indicated by the 

 large percentage of rutile and epidote in the latter. In his second con- 

 tribution to the subject the author describes the results of a separation 

 of the components of a fine clay by fractional levigation, and an ex- 

 amination of the separated portions. He concludes from his study 

 that nearly all the muscovite of slates, and all of the rutile bearing 

 variety, is a secondary product, subsequent in origin to the deposition 

 of the material from which the slates were formed.— The iron ores of 

 Sao Paulo, Brazil, are found in two principal districts, the Jacuj irai _a 

 and the Ipamena. In the first locality the ore, with a violet titaniferous 

 pyroxene, forms a schistose rock, in which perofskite, apatite and a 



