474 SCIENCE PROGRESS 



transition point sometimes recorded between iooo° and 1200 , 

 which they state is due to the presence of oxide. 



GEOLOGY. By G. W. Tyrrell, A.R.C.Sc, F.G.S., University, Glasgow. 

 General and Dynamic Geology. — The past climates of the earth 

 are dealt with by C. Schuchert (Carnegie Inst. Washington, 

 191$, Publ. No. 192, 263), who regards the principal climatic 

 variations as due to changes in topography, to variations in 

 the amount of heat stored in the oceans, and to changes in the 

 composition of the atmosphere affecting the storage of solar 

 radiation. 



The prismatic structure of igneous rocks is discussed by 

 R. B. Sosman, who distinguishes three general types (Journ. 

 Geol. 1 916, 24, 215). The commonest is that due to thermal 

 contraction in the solid rock. A newly distinguished mode is 

 due to convectional circulation of the magma whilst still liquid, 

 forming polygonal cells like those formed in cooling wax or 

 oil. A third type is produced by internal expansion conse- 

 quent upon alteration, producing the " weather-crack " (or 

 " onion-structure ") often seen in weathered diabase. 



Dr. L. L. Fermor and C. S. Fox have mapped in detail a 

 selected area (65 square miles) of the Deccan Traps in the 

 Chhindwara district, Central Provinces of India (Records Geol. 

 Surv. India, 191 6, 47, Pt. II. 81). The lavas rest directly on 

 Archaean granites and gneisses. Five flows were detected, 

 each of which is vesicular at the margins, and with coarse basalt 

 or dolerite in the central portions. The flows are separated by 

 small thicknesses of fresh-water fossiliferous sediments, or of 

 " green-earth," or of both together. The mapping shows that 

 the flows have been bent into a series of gentle folds. 



Petrology. — S. J. Shand has devised a simple and apparently 

 very efficient micrometer for the measurement of the quanti- 

 tative mineral composition of rocks by the Rosiwal method 

 (Journ. Geol. 191 6, 24, 304). The rock slide is fixed on a 

 sledge moved by micrometer screws fixed at both ends. The 

 instrument is mounted on the stage of the microscope. The 

 writer has found that an ordinary mechanical stage fitted with 

 a vernier gives very good and rapidly achieved results in this 

 kind of measurement. 



In a paper on the building of the North Atlantic Tertiary 

 volcanic plateau (Geol. Mag. (6), 1916, 3, 385) L. Hawkes dis- 



