TWO-PHASE CONVECTION IN IGNEOUS MAGMAS 489 
for syenite, and g per cent for granite.. The data need confirma- 
tion, as authorities disagreed as much as too per cent. The diffi- 
culty of accurate estimates has been shown by Day, et al.2. The 
expansion with temperature is estimated at 0.000025 volume per 
degree Centigrade, but is greater for liquids than solids. From 
these one may roughly estimate the proper order of magnitude as 
given in Table I, though the figures may be far from accurate in 
detail. Attention is called to the small differences due to tempera- 
ture alone as compared with larger ones due to a change from liquid 
to solid and to changes of composition. 
TABLE I 
APPROXIMATE SPECIFIC GRAVITIES OF PHASES IN MAGMaAs 
AT 1000° AT I100° 
Solid Liquid Solid Liquid 
Averages Granites.) se 4) 2.63 2.40 2.62+ 2.30 
OWantzere asst 2.60 Be Ob] 2.50 2.36 
Orthoclase............ 2.49— 2.2 2.48 226 
Average Gabbro.......... 2.92 25 Os 2.91+ 2.74 
Plagioclase, AbsAny,.... 2.58 2.41 2) a 2.40 
Plagioclase, Ab;An,.... 2.62— 2.46 2.61 2.45 
Magne titeaers eter 5.05 4.80 5.03 Anna 
SIOlivime seine oan he, the Bee 3.05 Bs De 3.04 
ANUPMESS 5 Sou bob boos Gon Bails 2.96 3.14 2.05 
ESTIMATING CONVECTION EFFECTS 
No formulas seem to have been developed which can be directly 
applied to the estimation of the rate of convection circulation. 
Daly uses an ingenious combination of calculations of (1) the rate 
of movement of small solid or gaseous spheres, (2) the size which 
is the limit of application of this formula, and (3) the relative rates 
for larger spheres. The essential differences between such move- 
ment of spheres and convection are, first, that the magma moves 
™R. A. Daly, ‘‘ Mechanics of Igneous Intrusion,” Am. Jour. Sci., XXVI (1908), 27. 
2A. L. Day, et al., ‘Determination of Mineral and Rock Densities at High Tem- 
peratures,” Am. Jour. Sci., XX XVII (1914), 1. 
3 C. Barus, “‘High Temperature Work in Igneous Fusion,” U.S. Geol. Surv. Bull. 
103. 
4R. A. Daly, Igneous Rocks and Their Origin, pp. 260-64. 
