112 
ELEMENTS OE GEOLOGY. 
lurian, to be explained in Chapters XXV. and XXVI., not 
only occur in succession in this one mountain, but their un- 
conforniable junctions are distinctly exposed to view. 
To begin with the oldest set of rocks, Xo. 1; they consist 
chiefly of hornblendic gneiss, and in the neighboring Heb¬ 
rides form whole islands, attaining a thickness of thousands 
of feet, although they have suflered such contortions and 
denudation that they seldom rise more th^n a few hundred 
feet above the sea-level. In discordant stratification upon 
Fig. 82. 
WNW 3' Qiieenaig (2G73 feet). ESE 
Unconformable Palaeozoic strata, Sntherlaiidshire (Murchison). 
1. Laurentian gneiss. 2. Cambrian conglomerate and sandstone. 3, 3'. Quartzose 
Lower Silurian, with annelid burrows. 
the edges of this gneiss reposes Xo. 2, a group of conglom¬ 
erate and purple sandstone referable to the Cambrian (or 
Longmynd) formation, which can elsewhere be shown to be 
characterized by its peculiar organic remains. On this again 
rests Xo. 3, a lower member of the important group called 
Silurian, an outlier of which, 3', caps the summit of Queenaig, 
attesting the removal by denudation of rocks of the same 
age, which once extended from the great mass 3 to 3^ Al¬ 
though this rock now consists of solid quartz, it is clear that 
in its original state it was formed of fine sand, perforated by 
numerous lob-worms or annelids, which left their burrows 
in the shape of tubular hollows (see Chapter XXVI., figure 
of Arenicolites)^ hundreds, nay thousands, of which I saw as 
I ascended the mountain. • 
In Queenaig we only behold this single quartzose mem¬ 
ber of the Silurian series, but in the neighboring country 
(see Fig. 83) it is seen to the eastward to be followed by 
Fig. 83. 
W E 
Diagrammatic section of the same groups near Queenaig (Murchison). 
1. Laurentian gneiss. 2. Cambrian conglomerate and sandstone. 3_, 3'. Quartzose 
Lower Silurian, with annelid burrows. 3a. Fossiliferous^ Silurian limestone. 
36. Quartzose, micaceous andgneissose rocks (altered Silurian). 
