292 Geological Society. 
Gilbert’s Bridge (in Glen Tilt), where the parallel-banded Moine 
gneisses can be traced passing slowly into the honestones, in which 
parallel banding is equally well shown. This is a well-known 
horizon in the Central-Highland sequence, lying next the white 
edge of the Highland Quartzite, forming, in fact, its original flaggy 
margin. These parallel-banded rocks are in many cases succeeded 
directly by a very impure phase of the Main or Blair-Atholl Lime- 
stone; but in places patches of other material intervene, of which 
the most important is a dark schist: this suggests a small hiatus 
at the margin of the Limestone, and a photograph was exhibited to 
show this hiatus. The conclusions drawn from this section are 
supported by the section seen below Gilbert’s Bridge, and a somewhat 
similar one in the Banvie Burn, north of Blair Castle. As before, 
there is clearly a small hiatus at the base of the Limestone. 
In order to ascertain the meaning and extent of this break in the 
sequence, an account is next given of the complete succession near 
Braemar, and it is then seen that at Gilbert’s Bridge the Little 
Limestone and part, or at times the whole, of the Dark Schist is. 
missing. The hiatus always tends to occur as an area is approached 
where the material forming the Moine gneiss thickens, and was. 
originally of a rather coarser or more sandy nature. 
Where, however, the section is complete, it is seen that the 
material of the Moine gneisses is the flaggy margin or top of the 
Central-Highland Quartzite; it is succeeded by the Little Lime- 
stone, above which is the Dark Schist, and then the Main or Blair- 
Atholl Limestone. 
Other sections along the line of change are described, showing the 
varying phases of the honestones, and in two instances their passage 
into Moine gneiss. There is a constantly-varying hiatus at the base 
of the Main Limestone, but in the whole 40 miles this never exceeds 
the omission of the entirety of the Biack Schist and the Little Lime- 
stone (of no great original thickness). This break in the sequence is 
of small importance, and, as already stated, often disappears as the 
material from which the Moine gneisses were formed became thinner 
and finer, or more of the nature of a mud. 
Evidence is then given to show that the honestones tended to 
become more sandy and to thicken south-eastward again, or in 
the opposite direction to that in which the Moine gneisses come on. 
From this the author concludes that the parallel-banded material 
was deposited in a series of fans; in the larger fans we have the 
material of the Moine gneisses; in the smaller that of the hone- 
stones. Both are simply the flaggy top of the sandstone now 
forming the Central-Highland Quartzite, and are in fact a passage- 
rock on its margin. Anything like an unconformity between the 
two is obviously impossible. 
