104 JOURNAL OF THE Iju'y, 



tallization of the mica ? With nothing to contradict this, we 

 might assume that the TourmaUne was formed first. I had no 

 sooner commenced to beHeve this, than I found crystals crossing 

 a fault in the mass of mica (probably caused by compression dur- 

 ing some of the earth throes which the rocks had endured), which, 

 upon one side, were above the continuous sheet, and, upon the 

 other side, below the same sheet. One piece of mica, which was, 

 I think, the richest in crystals which I have had, was nearly value- 

 less from the difificulty of getting a crystal out because of this 

 trouble. No matter what care I took, I shattered them. 



Some idea of the variety of forms found can be got from the 

 slides Dr. Bolles wall show you. I have never seen two that could 

 be said to resemble each other except in a general way. You 

 might say of one group that they were fan-shaped, of another that 

 they were palm-like, of another that they were plumose. The 

 variety is infinite. I have mounted nearly one hundred slides, 

 and I have examined under the glass probably three hundred, but 

 the variety is so great that I have felt unable to attempt a classifi- 

 cation by form. I hope you may appreciate my difficulty. I 

 know you would if I could have the pleasure of showing you the 

 collection. 



I should like to remark upon another of my questions. By 

 what I have learned of the laws of crystallization, I have been 

 taught to expect that the association of given elements, in given 

 proportions, will give a crystal having certain invariable features, 

 constant in its angles, manner of modification by twinning, etc. 

 The typical crystal of Tourmaline is a three-sided prism, having a 

 three-sided pyramidal termination, striated longitudinally, never 

 tapering in a detached crystal within my observation. I have 

 never but once seen a detached crystal curved. But the slides 

 show tapers, curves, etc., till they are bewildering. In the largest 

 of the enclosed crystals I have been unable to discover longitu- 

 dinal striation, and the form ofthe crystals has changed to a flat, 

 blade-like form, in some cases represented by a blade of grass. 

 Also, in most of my specimens the crystals are curved; the straight 

 are the exceptions. In the slide marked No. 3 is an exceptional 

 appearance, which I can only account for upon the theory of 

 alteration. You may agree with me by observing that the crystal 

 polarizes only in the thicker parts. 



