540 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



ture is peculiar in being remarkably poikilitic. The larger individuals of each 

 essential mineral contain smaller individuals of each of the other essentials as 

 well as crystals of the accessories except quartz and orthoclase. Those two 

 minerals are as usual the youngest of all. A few of the hornblende crystals 

 contain small cores of colourless augite. The specific gravity of a typical nodule 

 of this kind is 2-791, which is near the average for the Slesse diorite (2-806). 

 The nodule evidently has the composition of a basic hornblende-biotite diorite. 

 Its special structure could be explained on the hypothesis that it is simply an 

 inclusion of the Slesse diorite which has been heated and largely recrystallized 

 in the younger granodiorite magma. Since, however, these nodules occur in 

 parts of the batholith far removed from the diorite contact, and since they show 

 perfect interlocking with their host, it seems at least equally probable that they 

 are true basic segregations. If this second hypothesis could be proved we should 

 have one more illustration of the obvious consanguinity of the two batholiths. 

 The other kind of inclusion is of a much darker green-gray colour and is 

 also fine-grained. The essential components are a nearly colourless diopsidic 

 augite (very abundant), pale green hornblende, and labradorite, Ab 3 An 4 . The 

 accessories are magnetite, apatite, titanite, a very little biotite and quartz, and, 

 possibly, a little orthoclase. The structure is the hypidiomorphic-granular, but 

 at various places in the thin section suggests the diabasic structure. The specific 

 gravity of a typical nodule of this class" is 2-908. It has the composition of a 

 gabbro or of a basic augite-hornblende diorite. 



Contact Metamorphism. — The thermal metamorphism of the Carboniferous 

 sediments on the divide between Slesse and Middle creeks is intense, and is- 

 essentially like that noted as due to the intrusion of the Slesse diorite. A new 

 type of metamorphic product was found on the ridge north of Ohilliwack river, 

 about four miles from the lake. This is a hornfels richly charged with pheno- 

 cryst-like prisms of andalusite, which are shot through a mat of green mica 

 and quartz — a rock clearly derived from a silicious argillite. 



At the main contact of the granodiorite, on the ridge north of Depot creek, 

 a small patch of intensely metamorphosed limestone is cut by basic diorite dikes, 

 by the Custer gneiss-granite, as well as by the Chilliwack granodiorite. It is 

 probable that all three kinda of intrusive rock, especially the more acid ones, 

 have produced the observed recrystallization of the limestone. That rock has 

 the appearance of a typical pre-Cambrian crystalline limestone of Ontario or 

 Quebec. It is a white coarse-grained mass of calcite, bearing numerous scales 

 of graphite, epidote, and zoisite in rounded grains, cubes of pyrite and anhedra 

 of grossularite. 



Intrusives cutting the Volcanics. 



Besides the occasional andesitic and basaltic dikes which have evidently 

 originated in the same magma as the surface lavas, the Skagit formation is cut 

 by a small stock and by several wide dikes of quite different materials.* The 



* One highly vesicular, basaltic dike cutting the intercalated conglomerate may 

 be of distinctly later date than the Skagit volcanic formation. 



