10 
SILUKIA. 
[Chap. I. 
and chloritic crystalline rocks. In the absence of any fossils, provided with 
no classification (for some years elapsed before we entered into the stndy 
of the Silurian and Cambrian rocks), we necessarily failed to clear up the 
order, and remained in the belief of our precursors, that the sandstones 
and conglomerates forming the chief mountains on the west coast, and rest- 
ing upon buttresses of old gneiss, were simply the equivalents of the well- 
known Old Bed Sandstone of Scotland. 
This erroneous opinion continued to be upheld for many years, and was 
widely circulated in the justly popular and able work, 'The Old Bed 
Sandstone,' of the lamented Hugh Miller. The error was first removed 
by a survey of the western coast of the Highlands, which I made in 1854, 
and in which, at my request, Professor Nicol became my companion ; for I 
had long wished to ascertain the rationale of the singular succession I had 
seen, many years before, and wished to search out carefully the whole 
order of those rocks. Some of the results were communicated to the Meet- 
ing of the British Association at Glasgow. In the subsequent year (1855) 
Professor INicol added considerably to the value of the first survey ; and by 
his labours, combined with my own in a subsequent year, it was made 
manifest that the so-called ' Old Bed Sandstone' of the north-western 
coast was a rock of much higher antiquity than that which overlies the 
Silurian System ; for these sandstones and conglomerates of the west 
were seen to be overlain unconformably by those very quartzites and 
limestones which Sedgwick and myself had observed to pass with a south- 
easterly dip under crystalline rocks constituting the great mass of the 
gneissic schists and micaceous flagstones of the central and eastern High- 
lands. 
The question then arose, What is the age of those quartzites and 
limestones which have a much less crystalline character than the rocks 
by which they are overlain? In the quartzites MacCulloch had, it is 
true, discovered minute organisms, which he classed with Orthoceratites, 
and which are now known to be the infilled borings of Annelids and 
small Crustacea. It was not, however, until Mr. Charles Peach dis- 
covered, in the limestones of Durness, clear and unmistakeable fossils of 
various sorts, which in the hands of Mr. Salter proved to be the Lower 
Silurian fossils to be noted hereafter, that I became possessed of the key 
which I had long sought for, and by which I was at once enabled to 
develope the whole order of the North- Scottish succession, from a Funda- 
mental Gneiss upwards, through Cambrian and Lower Silurian rocks, 
to the Old Bed Sandstone. 
Seeing that the fossiliferous limetones of Sutherland were by no means 
the oldest of the Silurian deposits of my classification (being of younger 
age than the whole series of the Lingula-flags or " Primordial [Silurian] 
Zone " of Barrande), and that they reposed transgressively upon different 
members of the next underlying formation, or the red and purple hard 
