262 J.J. Harris Teall—Cheviot Andesites and Porphyrites. 
sites, as will be seen from the following analyses, and may probably 
be regarded as the plutonic representatives of these rocks. 
A 
B Cc 
Si0, SLs yy AOS OM Wea ele OAC 127 ook a eee ame 
Al,03 div ace, TAO RE 16°50 428) 
FejOg ice ee Ty ETI ec 20 tn 
FeO Saal Sake —_ Bess eer 4°26 Bae (ve 
CaO ARP 4°8 4°76 shen ae 5°97 
MeO RE 0 PRICING 25 
Na,O LI! A yeni yp Sar mS aammAR TE: as 
K.0 ree 129°) RAPP) Ag Aki eee 
Loss Ae AE ORO MER Meee O27 SOE 0°54 
100-1 101°26 101-05 
A Cheviot andesite. Analysis by T. Waller. 
B Quartz-norite, between Johannsen and Muttler. 
C Norite-Porphyrite from Tinnebach. 
B and C are quoted from the paper by Teller and von John. 
It seems strange that rocks of the Cheviot type have not been 
previously recognized among the older formations. It is not likely 
that they are as rare as this would seem to imply. A rock from 
Steinerne Mann, Nahe, bears a close resemblance, both macro- 
scopically and microscopically, to the Cheviot andesite. I have 
examined three slices, and in these there are 38 sections of pyroxene 
cut approximately parallel with the vertical axis of the prism; 30 of 
these extinguish parallel with the length of the section, a fact which 
seems clearly to prove the rhombic character of the predominating 
bisilicate. The pleochroism of these sections is much fainter than 
that of the corresponding sections in the Cheviot rock, but of the same 
character, and I am therefore inclined to regard the mineral as enstatite 
and the rock as enstatite-andesite; or, if the term andesite is to be 
denied to it on account of its Pre-Tertiary age, enstatite-porphyrite. 
This rock is labelled proterobase (melaphyre) by H. B. Stirtz, of 
Bonn, from whom I have obtained specimens, and proterobase by 
Mr. Samuel Henson, who also supplies the rock. 
Si02 EER AE EIN Sh WAS RAE PS 15/539) 0) 
Al,03 SOR BLOC llevoen ct wacten Resolna ere 17°44 
Fe,03* ap AR MT hs Be eee 6°50 
MnO 6 RATT CARS eas A ee trace 
CaO sachiby esa Vicia conv ike +e ybteas babes 7°82 
MgO bak ALLER ial, GRO R p Ld tae \Beae 3°10 
K:0 LE eee cee eer ene uence 1:98 
Na,O seal weet Vegas been GEE Mer ate 3°80 
Loss genitiiss dose hikari Ode 2°76 
100°93 
In conclusion, I would call attention to two other points of some 
importance in connexion with this examination of the Cheviot rocks, 
viz. first, the recognition of the fact that some of the normal porphy- 
rites are merely altered andesites; and secondly, the proof that in 
part at any rate the igneous rocks of Tuedian age, which occur in the 
neighbourhood of the Cheviots, belong to the basic series, and are 
therefore sharply to be distinguished from the rocks of intermediate 
composition which form so large a portion of the Cheviot district proper. 
* The total iron is estimated as Fe, O,. If allowance be made for the amount of 
iron undoubtedly present in the ferrous condition, then the excess in the analysis will 
be considerably reduced. | 
