260 J.J. Harris Teall—Cheviot Andesites and Porphyrites. 
Crystal No. 2. 
oP 0 Pe 22 est retlechion: 
172° 20! 2nd reflection. 
172° 233! mean. 
Or Oe 24a Pa =soeiae 
“‘ Now according to Naumann-Zirkel we have :— 
i aes JESS 
AALDIE foe, as Leak! hades) cee Bass, Gta yp secu ecec Re OMe 
Oligoclase so. ie aT ee ee can cemneS Oeat) 
Anorthite tM ih coe tee ghd eae RAcemnt en AUS Oa) 
(Labradorite) © pein iscsi ean) e-eigd ese gles ees oen OOmeet) 
“The first crystal, the more reliable, is within 9’ of anorthite; the 
second one very near oligoclase. The balance of evidence is there- 
fore in favour of a felspar nearly allied to anorthite.” 
Although these facts with regard to the chemical, optical and 
crystallographic characters of the Tynemouth felspars should properly 
appear in connexion with a description of the rock in which they 
occur, I have inserted them here because Mr. Waller’s observations 
appear to prove that the Stichill felspar belongs to the same species. 
To proceed with the description of the Stichill rock. The general 
characters of the felspars of the ground-mass are well represented 
in the Plate. Many of them appear as short, lath-shaped forms, 
which show the usual multiple twinning under crossed Nicols. The 
pyroxene occurs both in small grains and in large irregular plates 
with characteristic cleavages and extinctions. Its colour is a pale 
brown. It is interfered with by all the other constituents of the 
rock, and was evidently one of the last minerals to separate out. 
The alteration products have been already referred to in describing 
the olivine, and the only additional fact to be stated with regard to 
them is that the green substances have sometimes segregated in the 
form of irregular patches, one of which may be seen to the 8.E. of 
the centre of the lower figure, and that in these an indistinct radial 
fibrous structure may be made out (? Delessite). I have analyzed 
this rock with the following result :— 
Os lisse! Pe OREN RESET eceh S20 ths enn eerie 
AIO Wace seed drawing heen Wek ee a eee 
HaO3 fis osh sw vip aeeey. ean tiaan soci kas sgpitce on ase emmeOMCS 
FeO cass! Jadditl seus, ‘ae’ ahtete. ih tena \iees Qh Toned Pies mmmmCL ER 
MnO a) wc oak tins 84a Seseta tose © Meee i ceem imines "73 
CaO 8 () Bie. RUM ETE OLS Lis ed re een 
INA Oo \cec,, | Sac) tnt, fiwen So aeeb eed 5. wise.) eee Meee nee 
Ke a8 esses esi eon p toda] yea’ fee en: ces een 
PaO Ee) Teaeh ade dew vleve | tee! Yeas tee Mein ci eee mmm IERIE 
Legs'0n 19MI1ON f., ce 200 ) wee vse) SSPeAee lee 
99°94 
Specific gravity, 2°95 
It thus appears, both from the microscopic and chemical examina- 
tion, that the rock is not a porphyrite, but a representative of the 
basaltic family. It is pronounced a melaphyre by Prof. Rosenbusch, 
