1866.] J. GEIKIE — CAEMCK, AYKSHIEE. 527 



but very rarely with felstones. The more extensive rock-masses 

 present very much the same contour as the metamorphic felspathic 

 strata, forming rounded hills and knolls "with a somewhat lumpy 

 outline. 



Under the term dioritic are included all those rocks which consist 

 essentially of silicates of lime and magnesia set in a felspathic base 

 or matrix ; but a description of the many phases presented by the 

 class of rocks referred to is beyond the scope of this communication. 

 They show every gradation of texture, from a rock nearly compact to 

 dioritic masses in which the crystals often exceed an inch in length. 



The principal varieties are diorite and hypersthenite, both of 

 which are occasionally foliated. The felspar usually associated with 

 hornblende and hypersthene in these rocks is a hard white variety. 

 Diallage-rock occurs sparingly in one or two localities ; sometimes a 

 well-marked diorite exhibits crystals of white and clear quartz, and 

 thus becomes a syenite. 



Where the dioritic rocks are typically developed they are invari- 

 ably associated with serpentine. With this rock they exhibit inter- 

 esting junctions, to which reference will presently be made. 



ly. Seepentine. 



Serpentine rock abounds throughout the district ; it consists of 

 two principal varieties — foliated or schistose, and compact. 



1. Schistose Serpentine. — This is very plainly a bedded rock, and 

 is generally interstratified mth diorites. It varies in colour from 

 reddish-brown to green. The folia correspond with planes of bed- 

 ding ; but in some places the foliation is rude and irregular, and, 

 in the absence of well-marked dips in adjoining crystalline and 

 gritty beds, cannot always be asserted to coincide with original 

 lamination. Yein-like ramifications of diallage-rock, consisting of 

 masses of diallage-crjstals, sometimes intersect the schistose varie- 

 ties of serpentine. The joints are often abundantly coated with 

 soapstone, chloritic matter, and other silicates of magnesia and 

 alumina. 



2. Compact Serpentine. — This occurs in much larger masses. Dark 

 and pale green are its usual colours, but areas of red and beautifully 

 mottled green and red varieties are not uncommon. Sometimes it 

 is poryhyritic with diallage, and very frequently with bronzite. 

 Traces of bedding have seldom been observed in these rocks them- 

 selves ; but the trend of tlie masses agrees with the strike of the 

 rocks of the district, and interstratified lenticular beds of diorite are 

 of common occurrence, thus showing that the compact serpentines, 

 like the altered strata with which they are associated, are truly bedded 

 rocks. The association of serpentine with limestone will be ad- 

 verted to presently. 



A few notes upon the coast-section between Pinbain and Lendal- 

 foot may serve to throw some light upon the probable origin of the 

 serpentines of this neighbourhood. On the shore near Pinbain 

 occur some vertical beds of dark shales closely associated with a 



