148 CARNEGIE INSTITUTION OF WASHINGTON. 



(21) A new dip chart. Fred. Eugene Wright. J. Wash. Acad. Sci., 4, 440-444 (1914). 



In both structural and mining geology the problem frequently arises to 

 determine the direction, on a given vertical section, of the trace of a bed or 

 plane of knowTi dip and strike. The chart proposed in this paper enables the 

 observer to solve the problem directly with an accuracy of about 0.1°. The 

 chart is so constructed that the equation of which it is the graphical solution 

 is represented with as little distortion as possible. 



(22) The optical properties of roscoehte. Fred. Eugene Wright. Am. Jour. Sci. (4), 38, 



305-308 (1914). 



The optical data were obtained on unusually good material, kindly loaned 

 by Dr. W. F. Hillebrand for the purpose. Color, olive green. Luster, splendid, 

 almost submetallic and bronze-like. Cleavage, 001, perfect; 010, good. 

 Hardness between 2.5 and 3. Pleochroism, 7 = green brown, /3 = olive green, 

 a = olive green. Absorption, fairly strong, 7>j8>a. Refractive indices, 

 ^ = 1.704 ±0.003, /3 = 1.685 ±0.003, a = 1.610 ±0.003. Birefringence strong. 

 2£;;va = 42 to 69°; 2£z4 = 34 to 60°. Axial dispersion strong 2E^>2Et. 

 Optical orientation, 6 = 7, a :j8 = 0° or a small angle not over 4°. 



(23) The simultaneous crystallization of calcite and certain sulphides of iron, copper, and 



zinc. A crystallographic study. H. E. Merwin. Am. Jour. Sci. (4), 38, 

 355-359 (1914). 



The study of three occurrences of the sulphides of iron and zinc has estab- 

 lished with certaint}^ the deposition of marcasite, and with strong probability 

 the deposition of wurtzite contemporaneously with calcite. The marcasite 

 is definitely oriented with regard to the calcite and also the accompanying 

 pyrite. A close similarity between the crystallographic elements of pjTite and 

 marcasite is shown. 



(24) The thermal dehydration of stilbite, thaumasite, and the hydrates of magnesium 



sulphate and copper sulphate. H. E. Merwin. J. Wash. Acad. Sci., 4, 494- 

 496(1914). 



The method of locating sharp changes in the rate of dehydration of hydrates 

 by heating for definite periods at regularly increasing temperatures is applied 

 to substances which readily lose water in dry air at ordinary temperatures. 

 Two new hydrates of magnesium sulphate have thus been identified, and 

 stilbite has been shown not to be a definite hydrate. 



(25) Equations containing only one unknown constant to represent the parabola, the rec- 



tangular hyperbola, and certain exponential curves. H. E. Merwin. J. Wash. 

 Acad. Sci., 4, 467-469 (1914). 



The parabola is represented by 

 the rectangular hyperbola by 



^2 ^ *^2 *^1 



Vt-y Vi-yi 



+ C{x-x,) 



and ^^^-^ = ^^-^' C"-"i and ^^-^ = ^^-^' C'-'^ are exponentials. 



y^-y 2/2-2/1 y^-y yz-yi 



(26) The mode of formation of certain gneisses in the Highlands of New Jersey. Clarence 

 N. Fenner. J. Gcol., 22, 594-612; 694-702 (1914). 



The paper deals with certain geological phenomena which have been 

 observed in an area of ancient crystalline rocks in northern Ncav Jersey, and 

 discusses the manner in which the structures in question have originated. 



