110 SERPENTINE OF MONTVILLK, NEW JERSEY. 



mineral ia simply fibrous serpentine (chrysolite). The compact, light 

 yellow platy mineral coating the surface of the nodule to which I have 

 already alluded is found, od pulverizing and treatment with dilute acid, 

 a l 80 to be a mixtureof calcite and soft silky fibers of like nature. As 

 already intimated, I am disposed to consider this structure to have been 

 induced w holly by pressure. In the quarry dump were found fragments 

 of the rock, showing aggregates of serpentine, a very compact light 



enish amorphous mineral resembling deweylite, but with a specific 

 \ - it v of 2.5, small scales of deep reddish-brown and nearly colorless 

 mica, very compact aggregates of a greenish micaceous mineral with the 

 blow-pipe properties of vermiculite and other minerals, which for lack 

 of time and a sufficient amount of satisfactory material must be left for 

 future investigation. The secondary calcite. I should say. is usually 

 granular and of a slight bluish tinge. The mineral is, however, some- 

 times found in fibrous form and of a pure white color. 



In conclusion : The Montville serpentine is a highly hydrous variety, 

 approaching retinalite in composition, and was derived by a process of 

 meta8omatosis* from a mineral of the pyroxene group with the optical 

 and chemical properties of diopside. The change has been accom- 

 panied by a considerable increase in bulk, and in most cases the pro- 

 duction of beautiful slickensided surfaces and a platy structure due to 

 pressure. The excess of lime has recrystallized chieiiy as granular cal- 

 cite of a light bluish tinge, and also in fibrous forms. Other secondary 

 minerals have been found iu the quarry dump, but not having been 

 found in place have not "been worked out genetically. 



No free silica in the form of chalcedonic veins, such as are an almost 

 universal accompaniment of altered beds of duuite, have been found. 

 It is inferred that sufficient magnesia must have been furnished from 

 other sources to convert the whole into serpentine, or that farther 

 search will bring to light secondary silicate minerals. Concerning the 

 exact relationship existing between the pyroxene masses and the dolo- 

 mite. I am somewhat in doubt, as the outcrops were poor at the points 

 visited and the time limited. They are apparently segregations, and 

 certainly can not be considered in any way connected with igneous 

 agencies. A very small dike (less than afoot in width) of a dense, 

 ue, uly black trap rock occurs at the quarry opening, but apparently is 

 in no way connected with the processes of serpentinization. I presume 

 i his is the rock described as a porphyrite by Mr. Kemp in the annual 

 report of the state Geologist of New Jersey for 1880 (p. lll).t 



The derivation of ser pentine from pyroxene is a matter well known to 



•i use this word to indicate the process of "indefinite substitution ana replace- 

 ment;" ihr mum- in which it lias already been accepted by Dr. Hunt (Min. Phys., p. 

 i [unions, ami others. 



t It may be well to state that tin- quarry is the property of Mr. J. J. Gordon, <>f 

 Boonton, and can be at present easiest reached by rail from New York Citj to Boon- 

 ton and thence by carriages. The writer would here express his thank- to Mr. Gor- 

 don for his kin Iness in accompanying bim t > ti ■ quarry and forwarding desirable 

 material. 



