J. J. Harris Teall—Cheviot Andesites and Porphyrites. 261 
and would doubtless be called a dolerite by Mr. Allport. A rock 
of similar character occurs in the crag overlooking Dunsapie Loch, 
Edinburgh, where it is mapped as greenstone, the Stichill district 
being coloured porphyrite. 
CoNCLUSION. 
The most important result of this examination of the volcanic 
rocks of the Cheviot district has been the recognition in the pitch- 
stone-porphyrite of a rock bearing the closest possible relations 
structurally, mineralogically, and chemically, to certain of the so- 
called augite-andesites of Hungary, Transylvania, Servia, Santorin, 
and America.! Since my last paper was published, the first Bulletin 
of the U.S. Geological Survey has appeared, and it contains a full 
account of the researches of Mr. Whitman Cross on hypersthene- 
andesite, together with a sketch of the geology of Buffalo Peaks, by 
Mr.S.F.Emmons. The facts cited in this Bulletin appear to prove 
conclusively that andesites having a rhombic pyroxene as the pre- 
dominating bisilicate, are very widely distributed in space, and form 
a tolerably well-marked petrological group. It is not a little in- 
teresting that, just as the true character and wide distribution in 
space of this rock type is beginning to be recognized, evidence of 
its existence as far back in geological time as the Lower Old Red 
Sandstone period should be forthcoming. Thus suggesting the 
generalization that in petrological, as in organic types, a wide dis- 
tribution in space is associated with a wide distribution in time. 
We do not yet appear to have found in the Cheviot district the 
plutonic representative of these andesitic lavas. If they could be 
found, they would probably resemble some of the rocks described by 
F. Teller and C. v. John in their paper entitled “‘Geologisch petro- 
graphische Beitrige zur Kenntniss der dioritischen Gesteine von 
Klausen in Siidtirol.”? Typical norites are far too basic to have 
supplied the materials for these Cheviot lavas and tuffs. 
The igneous rocks near Klausen are intrusive in phyllite and 
gneiss, and are described by the authors above referred to under the 
terms norite, norite-porphyrite, quartz-norite, and quartz-mica-diorite. 
The rhombic pyroxene in the norites includes both hypersthene and 
enstatite, the former mineral being distinguished from the latter only 
by its more marked pleochroism. 
The norite-porphyrites occur at the boundaries of intrusive masses 
of the ordinary norite, and therefore differ in their geological rela- 
tions from the Cheviot andesite. They also differ from this rock in 
having a micro- or crypto-crystalline ground-mass, and not a glassy 
base. 
Chemically, however, the norite-porphyrites and the quartz-norites 
approximate in character to the Cheviot and other hypersthene-ande- 
1 Professor Bonney states that the rhombic pyroxene occurs in andesites from 
Pichincha, Antisina, and probably also Chimborazo. He is now engaged in an 
examination of the specimens collected by Mr. Whymper from these and other 
localities in South America. 
2K, K. Geol. Reich. 1883, Heft 4. 
