CHAP. XXXIII 
HISTORY OF INVESTIGATION 
n 
geology.” Portlock’s own description is still the most complete summary 
of the geology of that interesting region. 1 
"While such advances were being made in the knowledge of the structure 
of the volcanic rocks of the North of Ireland, the geologist had already 
appeared who was the first to attempt a systematic examination of the 
Western Islands, and whose published descriptions are still a chief source 
ol information regarding the geology of this extensive region. Hr. Mac- 
culloch seems to have made his first explorations among the Hebrides some 
time previous to the year 1814, for in that year he published some remarks 
on specimens from that district transmitted to the Geological Society. 2 For 
several years in succession he devoted himself with great energy and 
enthusiasm to the self-imposed task of geologically examining and mapping 
in a generalized way all the islands that lie to the westward of Scotland, 
from the remote St. Hilda even as far as the Isle of Man. From time to 
time, notices of parts of his work were given in the Transactions of the 
Geological Society. But eventually in 1819 he embodied the whole in his 
Description of the Western Islands of Scotland, including the Isle of Man. 
This great classic marks a notable epoch in British geology. Properly to 
estimate its value, we should try to realize what was the state of the science 
m this country at the time of its appearance. So laborious a collection of 
facts, and so courageous a resolution to avoid theorizing about them, gave to 
his volumes an altogether unique character. His descriptions were at once 
adopted as part of the familiar literature of geology. His sections and 
sketches were reproduced in endless treatises and text-books. Few simde 
works of descriptive geology have ever done so much to advance the pro- 
gress of the science in this country. With regard to the special subject of 
the present memoir, Macculloch showed that the basalts and other eruptive 
rocks of the Inner Hebrides pierce and overlie the Secondary strata of these 
islands, and must therefore be of younger date. But though he distinguished 
the three great series of “ trap-rocks,” “syenites” and “ hypersthene-rocks " 
°r “ augite-rocks,” and indicated approximately their respective areas, he did 
not attempt to unravel their relations to each other. Nor did he venture 
npon any speculations as to the probable conditions under which these rocks 
' eie produced. He claimed that those who might follow him would find a 
great deal which he had not described, but little that he had not examined. 
‘Subsequent observers have noted many important facts, of which, had he 
observed them, he would at once have seen the meaning, and which he cer- 
tainly would not have passed over in silence. But as a first broad outline 
0 the subject, Macculloch’s work possesses a great value, which is not 
essened by the subsequent discovery of details that escaped his notice, and 
o important geological relations which lie failed to detect. 
It has already been pointed out that some of the earliest and ablest 
o Jservations among the volcanic rocks of this country, especially in Scotland, 
vere made by foreigners. Students who had repaired from abroad to Edin- 
S ' J it '. p01 r ', L 011 tlle Geology of the County of Londonderry and parts of Tyrone and Fermanagh,” 
GmL Su ™V’ 1843. * Trans. Geol. Soc. yol. ii. 1814. 
