RECENT ADVANCES IN SCIENCE 29 



Stratigraphy : 



Knopf, A., A Geologic Reconnaissance of the Inyo Range and the Eastern 

 Slope of the Sierra Nevada, Cal., U.S. Geol. Surv., Profess. Paper, 110, 

 1919, p. 130. 



Thorpe, M. R., Structural Features of the Abajo Mountains, Utah, Amer. 

 Journ. Sci., 1919, 48, pp. 379-89. 



Baker, C. L., Contributions to the Stratigraphy of Eastern New Mexico, 

 Amer. Journ. Sci., 1920, 49, pp. 99-126. 



Field, R. M., The Middle Ordovician of Central and South-Central Penn- 

 sylvania, Amer. Journ. Sci., 1919, 48, pp. 403-38. 



Savage, T. E., The Devonian Formations of Illinois, Amer. Journ. Sci.. 1920, 

 49, pp. 169-82. 



Thomson, J. A., The Geology of the Middle Clarence and Ure Valleys, East 

 Marlborough, New Zealand, Trans. New Zealand Inst., 1919, 51, pp. 289- 

 • 349. 



MINERALOGY. By Alexander Scott, M.A.. D.Sc. 



Synthetic Mineralogy. — Since this branch of the subject was last 

 considered in these reports (Science Progress, 14, 38, 1919), 

 several papers of considerable importance have appeared. The 

 ternary system CaO— MgO— SiOa has been investigated by J. B. 

 Ferguson andH. E. Merwin(^mer./owrM. Sa.,48, 81, 1919). Since 

 two of the three binarysystems of the componentoxides are some- 

 what complicated, the ternary system, as might be expected, is 

 more complex than any of those hitherto investigated in the 

 Geophysical Laboratory, In addition to the simple oxides, the 

 forms stable in contact with the melt include three calcium 

 silicates, one of which is pseudowollastonite, the two magnesium 

 silicates, clinoenstatite and forsterite, and four ternary com- 

 pounds. Of the last, two correspond to the minerals diopside 

 and monticellite, while the other two are compounds which 

 have not been prepared hitherto, their composition being 

 SCaO . 2MgO . 6Si02 and 2CaO . MgO . 2SiO . The latter com- 

 pound is regarded as akermanite, as not only are the optical 

 properties in agreement with those of the Italian example of 

 this mineral, but the formula does not differ radically from 

 that (8CaO .4MgO .9Si02) ascribed to the natural material by 

 W. T. Schaller {Bull. U.S. Geol. Surv., 610, 109, 1916). Aker- 

 manite was regarded by J. H. L. Vogt [Mineralbildung in 

 Schmelzmassen, 96, 1892; Die Silikatschmelzlosungen, 1, 49, 

 1903), who considered it an essential constituent of melilite, 

 as calcium silicate, in which part of the lime was replaced by 

 magnesia. This explanation was negatived by the failure of 

 A. L. Day and E. S. Shepherd {Amer. Journ. Sci., 22, 280, 1906) 

 to find such a compound in their investigation of the system 

 CaO— SiOa, and the problem of the constitution of akermanite 

 has hitherto remained unsolved. 



Both monticellite and the compound 5CaO . 2MgO . 6SiO, 

 form solid solutions, but these, hke the pure compounds, tend 



