294 J. J. H. TEALL—-PETROLOGICAL NOTES ON 
(see Plate XII. fig. 2), indistinct brownish granules (? augite), and 
specks of magnetite imbedded in a clear isotropic glass. In the 
rock from the central portions of the dyke the felspars of the 
ground-mass and augite grains are much more fully developed, and 
the base itself also appears completely devitrified. The rock from 
the margin of the dyke bears a striking general resemblance to 
many of the so-called augite-andesites of Hungary and Santorin. 
Chemical Analyses of the Cockfield and Armathwaite Dyke. 
at Te TE RY: 
SUITE iE AM eR A a 57-57 58:07 59°25 56°10 
airrin itis (2 eaaeeas oe ene aa 13-22 16°75 17°24 
Herric' oxide. .20a5is.ess-ee2 6:04 : 4:00 ; 
ISEPOUS GRIGG 4 oh sas5.b-ae8 3°95 oo 4-82 a 
Manganese oxide ......... “21 =e ao Be 
TIAL pebble ed see tied 20 pA a 6°87 7:04 6°88 11-20 
Marnesian! 2.000: ts 40. ae 4-24 4-46 3°81 2-29 
Potash; <22:05 See 1-08 1-58 1-92 1:38 
Seda hich kh oh ee ere 2-98 2°59 2°56 2-04 
Sul hut + c.)-.2csspaaep: "19 He = + 
Carbonic acid... .....2...5. "30 sae trace 3°60 
Phosphoric acid........... 15 ies I 
Mitarne acids! jyi.0 WesS. e trace fee set si 
Waters. fo Poteet eh cee 1:25 1:50 os 1:55 
99-14 98-56 99-99 100:16 
I. Specimen from Great Ayton. Analysis by W. F. K. Stock, Esq., of 
Darlington*. 
II. Specimen from Armathwaite, about 60 miles from Ayton in a direct 
line. Analysis by W. F. K. Stock, Esq. 
III. Specimen from Great Ayton. Analysis by J. E. Stead, Hsq. 
TV. Altered specimen from the margin of the dyke at Preston. Analysis by 
J. EH. Stead, Esq. 
Note on the Action of Hydrochloric Acid on the Rock of the Cockfield 
and Armathwaite Dyke. By W. ¥. K. Srocx, Esq., Darlington. 
Tuer following investigation was suggested by the apparent ease 
with which a notable quantity of the Cockfield Armathwaite rock 
was acted upon by hydrochloric acid in open flasks, and by the 
fact communicated to me by Mr. James Anson, of Darlington, 
that sections cut by him showed a large proportion of matter 
wanting in definite form. ‘The Ayton rock was first examined. A 
portion was reduced to an extremely finely divided condition by 
long-continued trituration in an agate mortar. About 2 grammes 
of the fine powder were sealed up in a pressure-tube of strong 
Bohemian glass along with 20 ¢.c. of hydrochloric acid of sp. gr. 
1:16. The tube with its contents was exposed in an air-bath to a 
* This analysis of the Ayton rock was originally prepared for Mr. Anson ; 
but, thanks to the kindness of the latter gentleman, I am able to give it in this 
paper. 
