fourth inch in thickness. He very kindly furnished me with some for 

 analysis (see helow bl). He has presented me with a fine crystal of gray 

 corundum, about two-thirds of which is changed into damourite. Col. 

 Jos. Willcox, in his rich collection of American corundums, has several 

 good crystals, of which he very generously contributed the material for 

 analysis (see below, b2). 



c. Another very beautiful variety of the same mineral forms also 

 pseudomorphous crystals after corundum. The material for analysis 

 was from a fragment of a crystal, showing on two sides the remnant of a 

 pyramid. It contains a nucleus of gray corundum from which a very 

 fine scaly white pearly damourite is radiating, giving it a pseudo-fibrous 

 structure (c). 



d. The scales of damourite occasionally become so fine that they can- 

 not be distinguished with the naked eye and the mineral becomes massive, 

 sometimes globular, sometimes with a slaty structure, similar to talc 

 slate. This is often mixed with aggregation of larger scales of a greenisb- 

 white color and pearly lustre. Dr. Koenig has made an analysis of the 

 massive globular greenish-white crypto-crystalline variety (see below, d). 



e. A white or grayish-white variety of a fine scaly, often crypto-crys- 

 talline, structure, sometimes slaty, generally pseudo-fibrous, the apparent 

 fibres from one-half to over six inches in length, frequently invests the 

 granular grayish-white corundum. The lustre is generally very feeble, 

 otherwise pearly, inclining to silky. Scales of damourite of a white or 

 greenish color are disseminated throu-h the white fibrous mass, some- 

 times in small veins or accumulating into masses to a scaly granular 

 rock. An analysis of the pseudo-fibrous white damourite by Dr. Koenig 

 is given below (e). 



On one side and as a rule farthest from the corundum, it gradually 

 becomes dull-green and changes into pure granular chlorite. 



/. Xext to the corundum is generally another variety of damourite, 

 forming a seam between it and the white (c); it is from one-fourth to two 

 inches in thickness. 



Whilst crypto-crystalline and consisting of exceedingly minute scales, 

 they are arranged in fibres at right angles to the corundum. This variety 

 of damourite much resembles some kinds of serpentine. It has a yel- 

 lowish oil-green color, its lustre is waxy or dull. It is remarkable that 

 the slender crystals of tourmaline, which are frequent in the white 

 variety (e) and which'penetrate into the chlorite, have not been observed 

 in any of the numerous specimens which I had for examination. 



I shall give below my analysis of a sample, investing a mass of gray 

 corundum (/l), and the mean of two analyses by Mr. Th. M. Chatard 

 (/2), of a sample taken between the corundum and the white variety (e). 



g. The highly interesting pseudomorphs of damourite after corundum 



from Laurens District, South Carolina, probably occur in mica slate. 



I have already stated that most of the crystals of corundum from this 



locality are coated with a micaceous mineral, which the analysis proved 



A. p. s. — vol. xiii.— 2w 



