172 A Geological Trip. [Sess. 
is another layer, 200 to 300 feet thick, composed largely of 
fine white quartzite, so white and pure that it looks like loaf- 
sugar, and has had the term “saccharoidal” applied to it. In 
many parts it has a pink or reddish colour. In this series 
occurs the famous piped quartzite (Plate XIV. 4, 5), the 
pipes being composed of a quartzite somewhat harder than 
the matrix. They are supposed to mark former worm- 
burrows in the rocks, as they were being deposited in the 
soft state at the bottom of the sea. These markings are very 
abundant, and are a characteristic feature of the quartzites. 
Plate XIV. 6 shows a“ pipe” in longitudinal section. Above 
the layer of piped quartzites appear a series called the fucoid 
beds, 40 to 50 feet in thickness—so called from certain 
peculiar markings which the earlier geologists took for sea- 
weeds. These marks are now understood to represent the 
flattened castings of the various worms that swarmed at that 
period (Plate XV. 3). 
The careful examination of these beds, which are composed 
of calcareous shales and sandstones, with bands of rusty dolo- 
mite, has afforded evidence which establishes with a fair degree 
of certainty the true geological position of these rocks. Re- 
mains of trilobites have been found, and of one especially, 
termed Olenellus, which is particularly characteristic of rocks 
of Lower Cambrian age—that is to say, about as ancient as 
the lowest sedimentary rocks in Wales, and long supposed to 
be the very oldest. You will see the importance of this 
discovery : it stamps these series of rocks, beginning with the 
basal quartzites, as being of Lower Cambrian age (fig. 2, C) ; 
and you will have observed that these rocks lie unconform- 
ably on the edges of the Torridon sandstones ; and when you 
regard the enormous interval between the time the Torridon 
sandstones were laid down and the time when the quartzites 
were commenced, you may be able to form some slight con- 
ception of the venerable antiquity of these sandstones. In 
fact, as far as I am aware, they represent the oldest water-laid 
rock, of which we have certain knowledge, in the world. 
Above the fucoid beds we come to the band called the 
serpulite grit, thirty feet or so in thickness, which marks a 
shallowing for the time being of the sea where it was deposited. 
It is composed of massive grit, and in many parts the remains 
1 adage 
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