part 4] iN'ORiTE OF sieeea leoiste. 311 



an inch and a half in diameter ; they enclose felspar-laths more 

 or less completely, and this, in the case of the larger spots of this 

 type, gives rise to a beautiful ophitic structure. The brown spots 

 of the second type vary considerably in size, but they are generally 

 larger and of finer texture than those of the first type ; -they are 

 often irregular in shape, and of a reddish tinge. These patches are 

 altered and highly-corroded fragments of the older norite, and are- 

 naturally most numerous near the margins of the parent rock ; 

 they were saved from complete destruction onl}" by the freezing of 

 the invading magma. 



The younger norites formed several series of intrusions into the 

 older norite, but only two of them, referred to below as the first 

 and second series respectively, can be recognized with certainty. 

 The first of these, much smaller in volume than the second, was. 

 intruded after the older mass had largely cooled down ; conse- 

 quently it shows a chilled margin in many cases. It generally 

 possesses a texture similar to that of the main mass, but its. 

 characteristic colour and weathering, as well as the lack of banding 

 and jointing, readily distinguish it from the normal norite. Like 

 the intrusions of the later series, it generalh^ broke through the 

 older norite quite irregularly; nevertheless, cases do occur in which, 

 it took on the habit of the later dolerite-dykes and gave rise to a 

 rock, which, in the hand- specimen, is distinguished from the 

 coarser dolerites onl}' with great difficulty. Fortunately, the 

 relations of these rocks are made clear at several exposures wherein 

 the dole rite is seen to cut all phases of the norite (see below, 

 p. 317). The second and more important series is typically much 

 coarser than the older or normal norite, and is consequently coarser- 

 than the hrst series also. Since the exposed portions of the 

 second series ai'e probabl}^ oi^^y fl^e upper part of one or more 

 very large intrusions, this greater coarseness may be due either to 

 the greater volume and consequent greater capacity for heat and 

 higher temperature of the second* series,' or even to the preliminary- 

 heating of the older norite by the first series. Either one of these 

 causes would have enabled the second series to cool slowly, and 

 thus acquire a coarser texture. It is at least certain that the 

 second series contained an enormous reserve of heat, because to 

 it is due most of the extensive alteration produced in the older 

 norite. Another possible factor in producing the coarser texture 

 was the slight difference in composition, such as induced an even, 

 greater degree of coarseness in the next set of intrusions, and 

 caused them to crystallize as norite-pegmatite. 



Norite-pegmatite cuts both the older and the younger norites, 

 and takes the form of veins as much as 18 inches wide and irregular- 

 tongues several yards across : one of the latter has apparently 

 induced foliation parallel to its margin in the older or normal 

 norite enclosing it. The norite-pegmatite consists essentially of 

 augite and bronzite, with some felspar and a small quantity of' 

 m.agnetite. 



