434 
THE GEOLOGIST. 
REVIEWS. 
Air-hreathers of the Coal Period ; a descrijjtive account of the Hemains of 
Land-Animals found in the Coal Formation of Nova Scotia, with re- 
marks on their hearing on theories of the formation of Coal, and of the 
Origin of Sj^ecies. By J. W. Dawson, LL.D., F.E.S., F.G.S., etc., Prin- 
cipal of M'Gill University, Montreal. 
To Dr. Dawson geology is indebted for much progress in the knowledge 
obtained of the fossil botany of the Palaeozoic period, but his discoveries 
of reptilian remains and of air-breathing land-shells in the coal strata of 
Nova Scotia, are discoveries in value far beyond the usual estimation of 
new species and genera. They are fixed points in the scale of progress in 
our science, — distinct steps in the ladder of human information ; they teach 
important conclusions, and, rightly, their discoverer feels himself under an 
obligation to make them known as extensively and perfectly as possible 
to the scientific world. Although already the specimens have been more 
or less extensively illustrated in the pages of the ' Journal of the London 
Geological Society,' and have been submitted to the investigation specially 
engaged in the study of such remains, Dr. Dawson has found it impos- 
sible to bring out in this way all the details desirable, and to present a con- 
nected view of the facts. Hence the present publication, which is a revised 
reprint of articles published during the present year in the * Canadian 
iSaturalist and Geologist,' and illustrated with, besides the plates given in 
that journal, a photograph-plate of details of various Dendrerpetons and 
Hylonomi. Those who wish minutely to study this interesting subject, we 
must refer to Dr. Dawson's valuable brochure ; but we may here well give 
a brief abstract of its contents, and in doing this we shall show a more 
marked appreciation of the doctor's labours than by any amount of lauda- 
tory comments we could bestow. The animal poi^ulation of the earth 
during the older or palaeozoic period is known to us chiefly through the 
medium of remains preserved in rocks deposited on the bed of the ocean, 
in which there is but slight chance of finding relics of the animals of the 
land, even if such had existed plentifully on its bounding shores. Perhaps 
for this reason — perhaps because there were no land-animals — the organic 
remains of the Cambrian, Silurian, and Lower Devonian rocks contain, so 
far as animal remains are concerned, only those of marine species. In the 
Upper Silurian and Lower Devonian, however, land plants begin to ap- 
pear ; and in the Upper Devonian these are so numerous and varied as to 
afford a great probability that animals also tenanted the land. Indeed, Mr. 
Kartt, of St. John, has informed the author of the discovery of insect- 
remains on the rich plant-bearing Upper Devonian beds of that locality. 
It is true, also, that reptiles of high organization have been found in beds 
referred to the Upper Devonian, at Elgin, in Scotland. That there was 
dry land even in the Lower Silurian period, we know, and can even trace 
the former shores. In Canada the old Laurentian coast extends for more 
than a thousand miles from Labrador to Lake Superior, marking the 
southern border of the nucleus of the American continent in the Lower 
Silurian period. Along a great part of this ancient coast are other sand- 
flats of the Potsdam sandstone, affording very favourable conditions for the 
embedding of land-animals, had such existed ; still not a trace has been 
found. 
" .1 have myself," says Dr. Dawson, " followed the Lower Silurian beds up to their 
ancient limits in some localities, and collected the shells which the waves had dashed on 
the beach, and have seen under tlie Silurian beds, the Lam'cntian rocks pitted and in- 
dented with weather marks, showing that this old shore was then gradually subsiding; 
