468 TRANSACTIONS OF SECTION C. 
and orthoclase as well as considerable fragments of older tuffs are also present. 
The sedimentary rocks of the group consist of very hard siliceous grits which, 
on microscopic examination, often show the presence of fragments of volcanic 
rocks of the same general characters as the associated lavas. These fragments 
are generally larger in size than the accompanying fragments and grains of sedi- 
mentary origin, The whole of the group is characterised by the presence of 
numerous, often very fine, secondary quartz-infiltrated veins, and at one part in 
the sedimentary division these veins make up quite half the bulk of the rock. 
Two small masses of biotite granite containing much microcline break through 
the diorite immediately to the west of the area. With these the volcanic 
members of the group may or may not have a genetic relationship. 
As regards the age of these rocks, it is impossible to arrive at a very definite 
conclusion. They are manifestly younger than the diorite, but are probably 
considerably older than the oldest beds of the Old Red Sandstone of the adjoining 
area, The lavas being throughout of acid type, it is evident that they cannot 
be correlated with the interbedded andesites of the local rocks of Old Red Sand- 
stone age. 
5. On an Actinolite-bearing Rock allied to Serpentine. 
By A. W. Grips, M.A., D.Sc. 
This rock is associated with the intrusion of basic rocks in’ Belhelvie, 
Aberdeenshire. Towards the northern end of this mass, which consists of 
troctolites, serpentines and allied types, a rock is occasionally met with which 
differs in some respects from the varieties common in the district. In its most 
typical development it shows a large number of dark-green rounded spots set in a 
fine felt of paler green colour, full of glancing needles. Most of the specimens 
show a more or less clearly defined banding or schistosity. The affinities of 
the rock are somewhat obscure in hand-specimens. But under the microscope 
the dark spots are seen to represent olivine, which is still partly unaltered. 
but partly serpentinised, as well as granulitised and drawn out. The rest of 
the rock is largely made of actinolite in small crystal flakes; there are also 
present a green spinel, abundant magnetite, and sometimes other ingredients. 
In most varieties there is no trace of felspar. This rock passes into varieties 
in which the spots are much less obvious, and finally grades into a rock that 
might be described as an actinolite-schist. 
The exposures of this rock, so far as they have been mapped, lie mostly on 
the outer fringe of the basic intrusion, and therefore close to the line of junction 
with the metamorphic rocks into which the igneous rocks have forced their way. 
From its field relations and its general characters it is clear that it represents 
a type of the basic rock which has undergone actinolitisation on an extensive 
scale. The original rock from which it is derived must in most cases have 
been an olivine-enstatite rock, more or less completely serpentinised, or else 
a very basic troctolite. Although actinolitisation is widespread in this, as in 
other metamorphic areas, a rock of this particular type has not been noted 
in this locality before. It has nowhere been found in large mass, and seems 
essentially a marginal phase. The most prominent exposure yet met with is, 
or was, a clump in a field adjoining the Udny Road, immediately south of 
‘Skelly-hill Wood.’ This exposure has recently been entirely blasted away, and 
it seemed desirable to make a definite record of its occurrence. 
6. On the Origin of some of the Mica-Schists of Anglesey. 
By Epwarp GREENLY. 
In the south-east and centre of Anglesey extensive tracts of country are 
occupied by mica-schists in which it is a very rare thing to find any survival of 
original structures. They are holocrystalline rocks, usually with strong parallel 
structure, and composed essentially of quartz, alkali-felspars, and white mica. 
In certain compact varieties, however, especially about Y Graig, Holland Arms, 
traces of felsitic texture can be found. Dr. Teall, who has examined the rocks 
in the field as well as under the microscope, regards them as in all probability 
