ANALYSIS OF SERPENTINE. 551 



" This is the composition of serpentine, and the ophiolite of Roxbury is thus shown to 

 consist of serpentine and talc, intermixed with a ferriferous carbonate of magnesia ; the 

 compact asbestus of Dr. Hayes is nothing more than serpentine." 



The result from a comparison of all these analyses is, that the rock at Roxbury is a ser- 

 pentine of the usual character, penetrated by veins of ferriferous carbonate of magnesia 

 and dolomite. We cannot agree with Hayes and Hunt that there is no dolomite present. 

 Its peculiar crystalline forms are too well marked and too numerous in the bed, and 

 numerous large rocks quarried from the bed, to admit of doubt. Yet there may be large 

 slabs of the serpentine which contain no dolomite, and it was doubtless these that were 

 examined by these two chemists ; especially as those parts which contain the dolomite are 

 less ornamental, and are not often transported from the quarry. The magnesite forms 

 finer veins than the coarse bunches and veins of the dolomitic mineral. We have sub- 

 jected to analysis specimens of the dolomitic mineral, and find it to be a true dolomite. 

 We think it is as abundant as the purely magnesian mineral. 



Dr. Hayes made an examination of the serpentine at Proctorsville, etc., which we will 

 add in his own words : " This mineral [at Proctorsville] has been described as a serpen- 

 tine, and its physical characters generally entitle it to be so considered. It is traversed 

 by thin white veins, producing a variety in its otherwise deep-green color. The averages 

 of a number of samples are included in the following determinations : 



" IV. 100 parts of the Proctorsville serpentine afforded 



Moisture, ...... .40 



Carbonic acid, ..... 17.05 



Magnesia, ...... 16.00 



33.45 



As the cementing material, leaving 66.55 as basis rock, composed of 



Combined water, .... 6.21 

 Silicic acid, ...... 36.10 



Magnesia, 18.70 



Proto-perox. iron and manganese, . . 3.40 

 Alumina, ..... 1.13 

 Chrome iron, 92 



99.91 

 " V. 100 parts afforded 



Water, ...... 6.60 



Carbonate of magnesia, . . 28.40 



Basis rock, 68.00 



100.00 



" A number of similar determinations were made on the rock obviously composed of 

 talc and compact asbestus, cemented by a small proportion of carbonate of magnesia, in 

 an anhydrous state. 



" The serpentine of Newfane also afforded carbonate of magnesia, in variable pro- 

 portions. 



