258 
C. E. S. Davis. 
The ('onstitnonts present in seetions are siibangnlar (piartz (grain size 
0.1 niin. to 2 nun.), subordinate fresh inieroeline and a little slightly seri- 
eitised plagioelast', and rare aggregates of a flaky mineral of low bire- 
fringence' which may be kaolijiite, all set in a sericite cement. In weathered 
spc'cimens, plagioclasc' and sericite ai’o absent, but the clay constitiu'iit (a 
turbid, earthy mass) is abundant. 
The slate is a fiiu*-grained finely bedded micaceous rock. Fresh speci- 
mens are grey, and slightly weathered ones stained pink. It consists of 
sericite ami oval sliaped quartz grains about 0.05 mm. long, and a few small, 
rod-lik(* idioblasts of toiu'malim' iji caimnis stages of develoimu'nt (the- 
largest noted was 0.2 mm. by 0.1 mm.). The pJeochroic scheme of tin- tour- 
maline is X — deep blue-green, Z — very ])ale blue. 
H('dding of the slate is conspicuous and marked by orientation of tho 
sericite and by iron-staining. Although hand specimens of weathered slate' 
and of "shaly bands” from near the edge of the quartz “blow” resemble each 
othei', thc'y art' ^’('ry diftei'ent in seetion. “Redding’” is irregular in the 
•‘shaly bands,” flu; Hericit(' is haphazardly oriented and not associated Avith 
rounch'd quartz grains, ami (juartz occurs only in c'oins conqmsc'd of inter- 
locking angular grains. 
2. Sandstone. 
Rocks classed as “sandstones’* grade from sandy slates to porous- 
(juartzose grits reseml)ling the arkoses. Bedding, though clear in the finer 
grained rocrks, may not he noticed in the coarser ones. 
The dominant constituent is qiiartz, in rounded grains up to 5 mm. 
long with wavy extinction. Seri(dto, present in small quantities as a cement 
in all tli(‘ sandstones, is as common as (juartz in the sandy shales. Felspar' 
and tourmaline are rai'e, but rounded zircon ])lentiful. 
A f(;w ATins, consisting entirtdy of an interlocking mosaic of quartz,, 
thread the lower sandstone. Their grain size varies from about 0.1 to 0.5 mm. 
and in one specimen the grains of the vein (piartz Aveiv* not<‘d to be Im-ger 
than those of the surronnding sandstone. Rti-ain shadows may be noticed 
in the larg(‘r grains. Cherty lenses in the mi<ldle sandstone band have a 
conchoidal fracture and consist of tine (0.05 min.) intei'locking grains of 
quartz. 
As the lower sandstone is vei’y \-ughy also, it apjiears that material 
has been dissolved out of the rock to leave the vughs and has been redeposited 
elsewhere in the saim' bed as veins. The vughs (which are up to 3 cm. in 
diameter) are lined Avifli a thin layer of ((uai’tz, and within the vughs there 
are Avell dev(doi)ed crystals of barite up to 1 cm. long. A little barite is 
scattered through the sandstone, but no barite veins have been seen in this 
bed. IIoAvevtu*, in a cherty lens of the upper sandstone, there are barite- 
veins. 
Th(‘ nearby iuli'usion of })orphyritic cpidiorite, which cotitains a segre- 
gation (>[ bni'itc, is pro])ably tlie source of the barite found in the sand- 
stone. ft is suggested that Ijarito-ricli solutions dissoU’ed some material out 
of* the sandstoiu', forming tin* vughs Avhicb they later iiicrusled AAuth quartz 
and barile; this suggostioii may be tested by (inding out (at Armadale and 
soutliAvards) wh(*ther Ihe vugby sandstone is always baritic. 
