
648 STRATIGRAPHICAL GEOLOGY.  [Boox VI. — 
suffered in the denudation that provided material for the deep 
masses of Paleozoic sedimentary rock. 
The earliest system or connected suite of deposits in the Paleozoic 
series has received the name of Cambrian—a term first proposed by 
Sedewick for the most ancient sedimentary rocks of North Wales 
(Cambria).* By far the largest mass of these rocks is unfossiliferous, 
so that their identification in different countries is often entirely 
arbitrary. The extent and limit of the Cambrian system are 
probably best seen in the British Islands. 
-‘Rocxs.—The rocks of the Cambrian series present great uni- 
formity of lithological character over the globe. ‘They consist of — 
grey and reddish grits or greywackes, quartzites, and conglomerates 
with shales and slates. Their false-bedding, ripple-marks, and sun- 
eracks indicate deposit in shallow water and occasional exposure of 
littoral surfaces to desiccation. Sir A. C. Ramsay has suggested 
that the non-fossiliferous red strata in this system may have been 
laid down in inland basins, and he has speculated upon the probability 
even of glacial action in Cambrian time in Britain As might be 
expected from their high antiquity and consequent exposure to the 
terrestrial changes of a long succession of geological periods, 
Cambrian rocks are usually much disturbed. They have often 
been thrown into plications, dislocated, placed on end, sometimes 
cleaved and even metamorphosed. 
Lirz.—Much interest necessarily attaches to the fossils of the 
Cambrian system, for they are the oldest assemblage of organisms yet 
known. They form no doubt only a meagre representation of the - 
fauna of which they were once a living part. One of the first 
reflections which they suggest is that they present far too varied and 
highly organized a suite of organisms to allow us for a moment. to 
suppose that they indicate the first fauna of our earth’s surface. 
Unquestionably they must have had a long series of ancestors, though 
of these still earler forms no trace has yet been recovered, perhaps 
because the rocks in which any records of them might have been 
preserved seem to have been everywhere metamorphosed. Thus at 
the very outset of his study of stratigraphical geology the observer 
is confronted with a proof of the imperfection of the geological record. 
When he begins the examination of the Cambrian fauna so far as it 
has been preserved, he at once encounters further evidence of 
imperfection. Whole tribes of animals, which almost certainly were 
represented in Cambrian seas, have entirely disappeared, while those 
of which remains have been preserved belong to different and widely 
separated divisions of invertebrate life.? 
’ Much controversy has taken place in England in recent years regarding the re- 
spective boundaries of the Cambrian and Silurian systems. Into this controversy it is 
not needful to enter here. The limit which I have taken for the Cambrian rocks is 
that which appears to me to accord best with paleontological evidence. 
2 Brit. Assoc. 1880, Presidential address. 
* Recently the presence of medusee in the Cambrian seas has been detected in the ' 
casts of their forms found in Sweden by A. G. Nathorst. Svensk. Akad. Handl. xix. 
(1881). 
