J. J. Harris Teall—Cheviot Andesites and Porphyrites. 107 
No doubt the confusion has arisen out of the proposal of Prof. 
Rosenbusch to exclude rocks which do not contain olivine, or which 
contain it only in very small quantity, from the basaltic group. At 
present I am of opinion that the best way out of the difficulty is to 
regard the Meissner rock as a typical dolerite, and to use the term 
very much in the sense in which it is used by Prof. Sandberger, 
that is, so as to include the same rocks, without, however, attaching 
that importance to the presence or absence of ilmenite as compared 
with magnetite which he does. At any rate, if we exclude such 
rocks as the Rho6n dolerites from the augite-andesites, then we have 
remaining a group of porphyritic rocks with marked trachytic 
affinities, having silica per-centages ranging from 56 to 67, and a 
specific gravity of from 2°54 to 2-74. Our Cheviot andesite has 
a specific gravity of 2:57, and a silica per-centage of 63. 
CuremicaL ANALYSIS OF THE Cueviot ANDESITE. 
My friend Mr. Thos. Waller has been kind enough to make a full 
analysis of a specimen of the Cheviot rock, and this is given in the 
following table side by side with the analyses of certain typical 
andesites. It corroborates the views recorded in this paper, and 
brings the Cheviot rock into close relation with the Santorin lava of 
1866, the most important difference being the presence of a consider- 
able amount of water in the base of the former. 
A. Bees Caneel D. E. 
SIGE gt Reece or ere 63:0 63°05 | 58°76 66°62 to 67°35 62°76 
PAUMNTIUUTN a easccinclt oie 14:9 14°18 17°34 13°72 — 15-72 18-10 
Ferrous Oxide ......... : ; — 3°99 — 4:28 ! 
erricr Oxide vex. te... ou Oral ec 1:94 — 2°75 one 
DATO ie reas eee 4°8 5°40 7°46 3°40 — 3°99 6°03 
MASTICBIA J oneiee. stares. 2°8 1:12 2°67 0°96 — 1:16 2°59 
SCO het eA Rar Ree nee 4°0 5°65 2°36 3°79 — 5:04 3°45 
Potash : ef) 3°49 0°93 1:65 — 3:04 1°45 
MOSSE a aoM eeu cosas ee 4-0 2°04 | 2-10 0°36 — 0°54 se 
100-1 | 101-64 99°39 99°42 
A. Augite-andesite from the Cheviot district. Sp. gr. 2°54. Coquet, quarter mile 
above Windy Haugh. (Analysis by T. Waller.) 
B. Augite-andesite from Tokajer Bahnhof, Hungary. Analysis by V. v. Hauer, 
given by C. Doelter, Mineralogische Mittheilungen for 1874, p. 210. 
C. Porphyritic augite-andesite from Tuhrina, Hungary. OC. Doelter, Min. Mitt. 
1874, p. 205. 
D. Santorin augite-andesites. Analyses by C. v. Hauer, quoted by Zirkel, N eues 
Jahrbuch, 1866, p. 769. The specific gravities of three Santorin rocks are 
given in the same paper as being 27566, 2-544 and 2°507. (Specific gravity 
of Cheviot andesite, 2-53—2°62.) 
E. Andesite from the volcano of Rincon de la Viega (Andes), Dr. Otto Proeless ; 
Beitrige zur Kenntniss der Trachyte, Neues Jahrbuch, 1866, p. 652. 
In the next communication I propose to describe a few of the 
normal porphyrites and to discuss their relations to the true 
andesites. 
