aa oa gR Å TJ ma 
EUT on FREE ES TA 
Vv C 
NES SPOT 
WESTERN NOR, 
5 ' a 
CA N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 97 
silica, iron oxides, magnesia and sometimes alkalies are car- 
ried out from the magma to be deposited in the contact 
minerals formed at the boundaries or within the limestone 
masses. It may then be expected that the composition of 
the syntectic magma and its differentiates would be depen- 
dent on the nature of the contact minerals that are formed. 
If vesuvianite or grossularite or scapolite were formed 
in pure limestone, the magma must be deprived of much 
alumina, and one may expect aegirite or alkali amphiboles 
to be found in the resulting alkaline rock. If diopside, tre- 
molite or chondrodite are formed on a large scala, the igneous 
rock may have been enriched in alumina and Periape contams 
corundum. 
These are theoretical deductions whose verification has 
not been looked for. : Possibly they will'hot agree with facts, 
as these processes are so complicated and so many possibilities 
are open... It seems also to the writer that assimilation of 
limestone or lime-bearing materials with subsequent diffe-: 
rentiation must not by any means be the only possible way 
for the genesis of the alkaline rocks. Bowen has shown how 
such rocks may be possibly originate merely by differentiation 
processes from a gabbroid Sm oe MOT IRS sera EN in 
the presence of water 2). 
Convincing examples illustrating Daly's theory are 
quoted in numbers in his excellent monograph on the igneous 
"rocks ?) and do not need to be mentioned here. One of the 
most instructive cases is, however, just the Borolan laccolith 
already referred to, because it shows such close petrographic 
analogies to the sviatonossite. Shand has also in his wri- 
tings actually Fucgarted the possibility of assimilation of 
limestone ?). | 
Concerning the malignite from Poohbah Lake there are 
no indications in Lawson's paper ?) of limestone having been 
found in the surrounding country, which is said to be made 
1) N. L. Bowen, op. cit., pp. 55—66. 
2) R. A. Daly, op. cit. (New-York 1914). 
3) S. J. Shand. loc. cit. (Transact. Edinburgh Geol. Soc. IX, 1910) p. 413. 
2?) A. C. Lawson, loc. cit. (Univ California Bull. Dep. Geol. 1, 1896). 
7 
