179 
Angles between Optic Axes of Micas. 
1. Three Rock mica, ot as cite ones Se Oe 
2. Glendalough mica, .. . Bai bear (eae 3 
3. Mount Leinster mica, . . .. . 72 18 
2 Loagh Danimica, <. «<9. s 10s 0 
ee Glenidlure micz, °..' 2s ee OF EE 
“I have added to the determination of angles of the micas 
analyzed the optic angles of two other specimens of gray, trans- 
parent mica from Lough Dan and Glenmalure, county of 
Wicklow. 
« The four micas which were free from any intermixture 
of black mica have a high angle, while the angle between 
the optic axes of the mica from the Three Rock Mountain, 
which contained flakes of black mica, is nearly 20° less than 
that of the pure transparent gray micas. 
“<1 think that the uniformity of the preceding analyses is 
sufficient to show that Margarodite is entitled to be considered 
as a distinct species of hydrated mica, and that it is not merely 
an altered form of Muscovite, an opinion advocated by Mr. 
Dana, in the last edition of his ‘ System of Mineralogy.’” 
James Apjohn, M. D., made some remarks on Mr. Haugh- 
ton’s communication. 
The Secretary read a letter from Mr. Hornsby, Secretary 
to the Board of Works, presenting to the Academy Museum 
the following articles :— 
1. A small wooden bucket or situla, bound with bronze 
hoops, having perforated lozenge patterns. 
2. Ornamented bead, composed of blue glass, with bands 
of red and white glass. 
3. Bone bead or ornament. 
4. Fragments of bone comb. 
5. Neck and handles of an earthen jar. 
