XXXii INTRODUCTION. 
thickness it is equal to all of them put together—counting them from the May Hill sandstone 
to the highest beds of the dolomitic (or Pomfret) group (or Permian, if the word be limited 
as above) inclusive. Secondly. It is difficult of interpretation, especially from four causes. 
1. The first dificulty arises from the rarity of organic remains in the lower groups 
of the series, and from their apparent absence from the lowest. Should this negative 
result be confirmed, the lowest groups are then properly defined by Professor Phillips’s 
term, hypozoic. They are not merely azoic, or without any traces of former organic 
life; but they are hypozoic, or below the oldest rocks which have been found with such 
traces*. Hence arises a peculiar difficulty. We find traces of organic beings in some 
of our oldest rocks; but when did they begin? The answer to such a question is 
involved in inextricable obscurity; like that we meet with in tracing the origin of races 
and languages and institutions during the darkest periods in the history of man. But 
we have no comparable difficulty in tracing the history of the other subdivisions of the 
great Paleontological Series, such as the Silurian, Devonian, &c., up to the Tertiary. 
For each subdivision has some defined physical boundary; and a more or less defined 
Fauna, which has a relation to two other /auwnas—one above it, and the other below it. 
Nor is this all. As a great fact in the natural history of the earth, in comparison 
of which the exceptions to it sink into insignificance, great groups of species have 
disappeared, and new types of organic life have begun; not as a consequence of a vast 
lapse of time incompatible with the longer continuance of certain species, but in consequence 
of a change of physical conditions; and, as a general rule, these changes of conditions 
are marked by a defined succession of physical monuments, which are among the most 
instructive and fundamental phenomena in geology+. The study of such successive monuments 
is, and has been, the first great work of geology in which Paleontology has been but 
her handmaid. Without such successive monuments, Palzontology is only a supplement to 
zoology; and, in that point of view, it gives us no indication whatsoever of epoch, or date, 
or physical revolution in the past history of the earth. 
2. The neat difficulty in the analysis of the older Paleozoic rocks arises (at least in 
England) out of the general prevalence of cleavage-planes. Till these planes are un- 
derstood and distinctly separated from the beds (and also from the divisional joints, 
* In some of the grand sections of North America (exhibited to the Geological Society by Mr Logan) the Potsdam 
sandstone and other groups which are here called Cambrian rest unconformably upon a vast series of contorted meta- 
morphic rocks containing phosphate of lime in great abundance. If this fact were assumed as a proof of the original 
existence of organic beings in these old rocks, before they became metamorphic, it would, I think, prove that there were in 
America the traces of a Paleozoic group that was probably older than the oldest of those enumerated in the above Tabular 
View. But I amnot in this Introduction discussing metamorphic rocks, or leaning on any evidence that does not properly 
belong to the British series. 
+ The opinion stated in the text has always been held by myself; not as a consequence of any theory, but as a fair 
induction from intelligible facts. It was vindicated many years since by M. Elie de Beaumont. In more recent times it 
has (with certain modifications) been upheld by Professor E. Forbes: but his cheering and powerful help, on this and all 
kindred subjects, is now alas taken from us, to the deep sorrow of every British lover of natural science! But his name 
is cherished among the good treasures of our memory; and his works will be honoured, long after all the men of this 
generation haye passed away, and long after many of them have been forgotten. 
