1888.] 
Dr Stecher on Contact- Phenomena. 
167 
Distance from 
the Junction. 
Salisbury 
Crags. 
Found Point. 
Stewartfield. 
Pier, Aberdour. 
Heart. 
All nntwin- 
ned. 
All untwin- 
ned. 
4-5 feet. 
Untwinned : 
twinned = 16 ; 3, 
&c. 
2 feet. 
About half are 
twinned. 
j 
1 From the vicinity of an 
enveloped fragment. 
J 
The slice is per- 
pendicular to 
the junction. 
Mostly- 
twinned. 
4 inches. 
Seldom twin- 
ned. 
1 inch. 
Twinned : un- 
twinned =4:3. 
1 inch. 
Mostly twinned. 
From the im- 
mediate junc- 
tion. 
Nearly all 
twinned. 
So far as I am aware, such a relationship has not hitherto been 
noticed; nevertheless, I suppose that a similar dependence might 
also be established at other localities as well as in other rocks. I 
have already visited a great many localities in Saxony, Bohemia, and 
Thuringia, where augitic volcanic rocks occur in junction with the 
associated rocks ; yet in the few cases where I found the volcanic 
rock fresh up to the contact, I never succeeded in detecting this 
interesting phenomenon. Bor in none of these cases did the volcanic 
mass exhibit any modification of its structure towards the junction. 
There appears to be evidence that the associated rocks, where ex- 
amined, have exerted no cooling influence on the igneous magma, a 
condition which would be necessary for the production of such 
variations in crystalline structure. 
As will be seen in the above table, the proportion of twinned 
individuals of augite not only increases towards the junction 
with the contiguous rocks, but also depends on the distance 
from the junction with included fragments, so far is these have a 
considerable size. In the latter case this twinning of the crystals is 
found within a smaller distance. 
