320 



SCIENCE 



[N. S. Vol. XXXI. No. 791 



being no reversal of lateral gradient, the deflective 

 force becomes relatively much more efficient in 

 inducing lateral currents. 



The Missouri River, studied for comparison 

 with the rivers in higher latitudes, shows evidence 

 of unbalanced lateral erosion in the distribution 

 of its flood plain with respect to its course. 



Winds, crustal warping and asymmetry of drain- 

 age basins are other causes which may unbalance 

 lateral erosion, but conditions do not point to 

 their operation in the cases mentioned. The 

 unbalanced erosion in the Alaska rivers, there- 

 fore, seems undoubtedly due to the deflective force 

 of the earth's rotation. 

 Geologic Thermometry: Fred. E. Weight. 



In ordinary thermometry, temperature, or the 

 degree of hotness of a body, is defined by the 

 expansion of a perfect gas and is expressed in 

 terms of fixed units, determined by the freezing 

 and boiling points of water under standard con- 

 ditions. Temperatures are ascertained practically 

 by means of thermometers which, although they 

 vary greatly in type, are all based on some prop- 

 erty which varies in a definite way with the tem- 

 perature. In geology, temperatures are of funda- 

 mental importance, particularly the temperatures 

 to which rocks were heated in past geologic ages 

 and under inaccessible conditions. Points on the 

 geologic thermometer scale must therefore be his- 

 toric points, or temperatures at which permanent 

 changes occur in the rock or mineral, traces of 

 which persist at lower temperatures. Such defi- 

 nite points serve to establish limits within which 

 observed reactions must have been efi'ected. The 

 factors which may serve to furnish points of this 

 nature are, especially: melting temperatures of 

 stable minerals and of eutectics; inversion tem- 

 peratures of minerals; temperature limits beyond 

 which mouotropic forms can not exist under dif- 

 ferent conditions of pressure; stable ranges of 

 enantiotropio forms and of minerals which disso- 

 ciate or decompose at higher temperatures; tem- 

 peratures beyond which any physical property 

 acquires a permanent set and by virtue of internal 

 friction or other cause does not return to its 

 original value on cooling; also the occurrence of 

 zonal growth in isomorphous mixtures like the 

 feldspars or pyroxenes. These factors can be and 

 are being determined by modern laboratory meth- 

 ods and are in turn directly applicable to the 

 study of rocks. In applying such data geolog- 

 ically, however, it should be remembered that the 

 data are obtained under certain definite condi- 

 tions while in nature the rocks may have been and 



often were formed under totally different condi- 

 tions of equilibrium. Two factors particularly 

 may be operative in this direction, pressure and 

 solution, or the presence of other components, as 

 water, which tend to modify very materially the 

 equilibrium criteria and behavior of the physical 

 chemical system in question. The data now avail- 

 able on the geologic thermometer scale indicate 

 that the establishment of such a scale is feasible 

 and can be accomplished by a sufficient number 

 of proper laboratory determinations; also that in 

 many cases the application of such data to natural 

 phenomena is warranted. 

 Tlie Origin of the Pegmatites of Maine: Edson 



S. Bastin. 



The pegmatites of Maine all belong to the type 

 commonly known as granite pegmatites. The fact 

 that their chief minerals are also the dominant 

 minerals of the granites, the presence of granite 

 in all districts where pegmatites occur, and numer- 

 ous observed transitions from granite to pegma- 

 tite, indicate that the pegmatites are closely re- 

 lated to the granites in origin. 



The peculiar textures exhibited by the pegma- 

 tites as compared with the granites are not be- 

 lieved to be due mainly to differences in the pro- 

 portions of the principal mineral constituents or 

 of the rare elements such as fluorine, lithium and 

 phosphorus, but probably to greater abundance 

 of gaseous constituents in the pegmatite magma 

 as compared with the granite magma. The prin- 

 cipal gaseous constituent was probably water. 

 There are field indications that the pegmatite 

 magmas locally exhibited a considerable degree of 

 viscosity, sufficient for example to float fragments 

 of the schist wall rock. This and other facts 

 suggest that the vaporous content of the pegma- 

 tites was not so greatly in excess of that of the 

 granites as has commonly been supposed. Experi- 

 ments by F. E. Wright and E. S. Larsen on 

 specimens collected by the writer from the peg- 

 matites of Maine show that the quartz from the 

 finer-grained pegmatites and from the graphic 

 granite of the coarser pegmatites crystallized 

 above 575° C, whereas that of the large areas of 

 pure quartz, the quartz crystals, developed in 

 miarolitic cavities and the quartz associated with 

 tourmaline, lepidolite, spodumene, etc., near the 

 pockets in the gem-bearing pegmatites, was formed 

 below 575° C. This fixes the temperature of crys- 

 tallization of many of these pegmatites at about 

 550° and 600° C. 



Feanqois E. Matthes, 



Secretary 



