232 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
cation of the triclinic substance within the orthoclastic distorted it latterally ; 
and that the open structure in all felspars in which the angle departs from 90° is 
in a double sense an outcome—due to the removal of a material soluble ina 
solvent incapable of attacking the orthoclase. 
I have somewhat particularly described this structure, as I have known it 
to be mistaken for that striation which is founded on by some geologists as a 
reliable criterion in the discrimination between orthoclase and the plagioclastic 
felspars ;—the following distinctions may, however, be pointed out :— 
The structure differs from the striation of twinning in that its markings are 
not rectilinearly parallel, but in undulating lines, —more undulating in ¢ than in 6; 
they cross the face c,—being at right angles to the macrodiagonal, while the 
lineation of repeated twinning is parallel to the macrodiagonal ; they are not 
alternately lustrous with the other parts of the crystal on revolution on an axis 
parallel to their own strike ; they are coalescent ; and they are lighter in colour 
than the rest of the crystal. 
I might add that, as these markings are as frequently seen in these vein 
orthoclases, as striation is in the plagioclastic felspars, they are as good a mode 
of discrimination between the two as the latter; and as they have never been 
seen in a plagioclastic felspar,-while striation may occasionally be seen in every 
plagioclastic felspar, where seen they give some absolutely specific information, 
which striation can never do. 
As the hemitropism of the crystals of amazonstone exhibits this singular 
structure in a modified development, it calls for notice. 
This amazonstone, as before noticed, is frequently in hemitrope crystals 
which are pervaded throughout with the corded structure, and to such an 
extent that the white opaque filamentous matter acts as tenons to the two 
halves of the hemitrope, binding them together, until separated by force ; when 
the white substance is seen with fractured edges like ruptured tenons, or the 
broken dovetails of the separated sutures of the disconnected bones of a skull. 
Thefacesof theseparated halvesof the hemitrope arefound to be highly polished 
and lustrous; the white ruptured lines passing across them in relief or depression, 
according to where the fracture operated,—like the rugosities of asingle-struck file. 
On pressing the two halves together, a certain amount of cohesion is re-estab- 
lished, as in the forcible reinsinuation of the sutures of the bones of the skull. 
Difficult as it is to account for the arrangement of the molecules during the 
thrawn polarity which is operating whilst a twin or hemitrope crystal is being 
built up, here is something more difficult still: for, across the path of the mole- 
cules of the green matter, while moving towards their appointed positions, there 
must simultaneously have been moving those other white molecules engaged im 
their work of building up an inosculatory net-work. A system of net-works 
rather, extending not like the float of the fisherman in single line, but im 

