108 ftPOLIA ZEYLANICA. 



range of types varj'ing much in relative acidity have neverthe- 

 less a very similar appearance in the field, and we pass by gradual 

 transitions to rocks having the composition of norites (labrado- 

 rite-hypersthene rock) and c?/oriYes (hornblende-labradorite rock), 

 &c. Most of these less acid types might also be called pyroxene 

 granulites. The most basic types occur chiefly as leuticles and 

 " pinched " bands amongst medium and acid types ; they include 

 rocks of which the principal constituents are hypersthene,augite, 

 garnet, basic plagioclase, &c. It is generally more or less evident 

 that these most basic types are to be regarded as amongst the 

 earliest products of the granulite magma. 



Rocks of anomalous or unusual composition are sometimes met 

 with, e.g., a felspar corundum rock from near Kandy, and a 

 garnetiferous leptynite in which spinel is very abundant ; atten- 

 tion may also be called to the remarkable rocks containing 

 corundum, sillimanite, &c., described by Professor Lacroix. There 

 occur also in the Balangoda district certain zircon granites con- 

 taining a large quantity of well-crystallized zircon ; little is known 

 as to the relations of these rocks ; it is not unlikely that they 

 may have some connection with the occurrence of a group of 

 rare minerals (including uraninite, &c.) found in the Balangoda 

 district ; they are probably intrusive in the charnockite series. 



Pegmatite Dykes, consisting essentially of orthoclase and quartz 

 with mica or hornblende or both, are found occurring as dykes 

 crossing the granulite foliation planes and as sills running along 

 these planes. The pegmatites must be in many cases regarded 

 as segregation veins ; they appear to have crystallized before the 

 cooling of the matrix, as the minerals are interlocked at the 

 junction, which is rather a transition than an abrupt junction. 



An important series of rocks not yet referred to is that of 

 the crystalline limestones. These rocks are found intimately 

 interbanded with the ordinary granulites, the beds of limestone 

 varying in thickness from hundreds of yards down to a few 

 inches. Many varieties are dolomitic, but there is great variation 

 in this respect. Many interesting accessory minerals occur, such as 

 phlogopite,forsterite, graphite, spinel, apatite, amphibole, clinohu- 

 mite, &c. The nature and origin of these rocks is exceedingly 

 obscure. Many would perhaps regard them as the highly 

 metamorphosed remains of some ancient calcareous sedimentary 

 series included in the vast mass of granulites, and owing their 

 characters to the effects of contact metamorphism. There are, 

 however, great difficulties in the acceptance of such a view. 

 Amongst these may be mentioned the, on the whole, small 

 quantity of the limestone compared with the vast bulk of the 



