434 



THE GEOLOGIST. 



REVIEWS. 



Air-breathers of the Coal Period ; a descriptive account of the Remains of 

 Land-Animals found in the Coal Formation of Nova Scotia, with re- 

 marks on their bearing on theories of the formation of Coal, and of the 

 Origin of Species. By J. W. Dawson, LL.D., F.R.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, bnt 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 j r ear in the * Canadian 

 Naturalist 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 population 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. 

 Hartt, of St. John, has informed the author of the discovery of insect- 

 remains on the rich plant-bearing LTpper Devonian beds of that localit}". 

 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. 



" I 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 the Silurian beds, the Laurentian rocks pitted and in- 

 dented with weather marks, showing that this old shore was then gradually subsiding; 



