Vol. 58.] CRYSTALLINE LIMESTONES OF CEYLON. 413 
large enough to enclose portions of more than one ‘finger’ of dolomite. 
Fig. 6 is from a specimen in which the intergrowth is less fine- 
grained than usual; it often sinks to quite microscopic dimensions, 
and such examples have been described by Prof. Lacroix * and 
Mr. Parkinson,” though without explanation. 
Fig. 6.—Ramifying or graphic intergrowth of calcite (C) and 
dolomite (D). x94. 
= 
[MA= Maonetite; MI=Mica.] 
In many of the parallel intergrowths the calcite and dolomite 
are of equal relative importance; in others, and in most of the 
ramifying intergrowths, we usually find that calcite predominates, 
and should speak of the dolomite as forming parallel or ramifying 
inclusions in the calcite; it is exceedingly rare to meet with a 
reverse relation. 
A conspicuous feature is the limitation of twinning to the 
calcite, the twinning-bands in it ceasing at the junction with 
dolomite, even when the two have a common optical orientation. 
Very seldom traces of twinning are found in the dolomite, and it 
seems perhaps to be not quite invariably present in the calcite, 
though usually so. 
The distinctness of the intergrowths, even on a very small scale, 
shows probably that the carbonates consist of pure dolomite or pure 
calcite, and that intermediate types are absent. 
: Bull. Soc. frang. Minéral. vol. xii (1889) p. 387 & fig. 60. 
* Quart. Journ. Geol. Soe, vol. lvii (1901) p. 205. 
