338 RECORD OF SCIENCE FOR 1887 AND 1888. 



of the purely chemical origin of the mineral, has been investigated by 

 Dr. George H. Williams and proven beyond doubt to be an altered 

 peridotite, and eruptive. The second and equally striking case of the 

 secondary origin of the mineral has been furnished by the present 

 writer,* who investigated the well-known serpentine locality', Montville, 

 ]Sew Jersey. The stone occurs here associated with a coarsely crystal- 

 lized dolomite in such a wa.y as to at once declare an origin from some 

 other source than from an igneous rock. The mineral proved here to 

 be also metasomatic, "a product of indefinite substitution and replace- 

 ment," after a non-aluminous pyroxene near diopside in composition. 

 The occurrence is so strikingly like that of the serpentines associated 

 with calcareous rocks, as described by Dr. Hunt, and also the serpen- 

 tine of the well-known eozoon, as to render it almost a foregone conclu- 

 sion that in all these cases the serpentinous material is of similar origin. 



The number of mineral species recognized as occurring either as acci- 

 dental or essential constituents in rock masses is naturally found to 

 increase as the rocks are studied in greater detail and as methods and 

 instruments are brought to greater perfection. Professor Eosenbusch, 

 in his Hulfstabellen zur Mikroskopischen Mineralbestimmung, gives 

 upwards of one hundred and seventy varieties, of which the optical and 

 micro chemical properties are sufiQciently well known for their determina- 

 tion in the thin section. Among the more interesting occurrences of 

 the rarer or little noticed of these may be mentioned the following: 



The rare manganese epidote or piedmontite has been described by 

 Prof. Bundjiro Kotot as a characteristic constituent of certain schists 

 of unexpectedly wide distribution in the ArchiBan system of Japan. 

 The typical piedmontite schist is described as consisting essentially 

 of piedmontite associated with fine quartz grains and with accessory 

 muscovite, greenish-yellow garnet, rutile, feldspar (probably orthoclase), 

 blood-red iron glance, and also opaque crystals of the same mineral. 

 The glaucophane rocks also carry it to some extent. The same mineral 

 has also been noted by Professor Haworth as occurring sparingly in the 

 quartz porphyries of southwestern Missouri in the United States. The 

 allied mineral allanite, first noted as a common constituent of many 

 granites by Messrs. Cross and Iddiugs, has been observed by Cross | 

 as a constituent of the quartz porphyries of the Leadville region, and 

 has also been described by W. H. Hobbs § in the form of parallel inter- 

 growth with epidote, as a characteristic constituent of a granite porphyry 

 from Ilchester, Maryland. Graefit|| has noted the presence of laavenito 

 in the elseolite syenites of Brazil. Cohen ^ calls attention to the fact 



*Pi-oc. U. S. Nat. Mus., 1888, p. 105. 

 + Quar. Jour. Geol. Soc, August, 1887, No. 171, p. 474. 

 t Geol. aud Miniug Industry oT Leadville, Coloi'ado, p. 329. 

 ^ Jolius Hopkins Univ. Circular, April, 1888. 

 II Neues .lahrb., 1887, i B., 2 Ileff, p. '^Oli 

 II Neues. Jalirb., IKS", ii B., p. 178. 



