July 23, 1908] 



NA TURE 



267 



In the biological section the author deals mostly 

 with the land faunas and Horas ; for their evidence is 

 naturally the most significant regarding former land 

 connections. But the marine fauna also gives weighty 

 evidence. The writer pointed out in 189 1 that the 

 relations of the echinoid faunas of North America 

 and Europe gave convincing evidence of a middle 

 Cainozoic land connection across the Atlantic ; and 

 the position then indicated for the North Atlantic 

 shores from the migrations of the sea urchins corre- 

 sponds to the general position assigned to it by 

 Dr. Arlt from the migrations of land animals. In 

 his statement of the biogeographical evidence, Dr. 

 Arlt follows the method of Blanford's fine address to 

 the Geological .Society in 1890. He considers the 

 existing distribution of each group of land organisms 

 in connection w;ith its geological history and with the 

 probable distribution of land and water on the earth 

 during its development. He illustrates the land routes 

 available for migration at successive periods in the 

 history of a group by an ingenious series of diagrams 

 {e.g. plate ii.). Dr. Arlt devotes 300 pages to a 

 summary of our knowledge as to the geographical 

 distribution of Cainozoic life. For the existing bio- 

 logical regions he adopts the division into three, and 

 the names he uses suggest the age of the faunas 

 and floras that inhabit them. The Holarctic region 

 he names Kainogaea, on account of the modern char- 

 acter of its life ; the Ethiopian and Oriental regions 

 he groups together as Mesogsa ; and for the remain- 

 ing regions, including Australasia, Madagascar, and 

 the Neotropical region, he adopts, with a modified 

 meaning, Dr. Sclater's name, Palaeoga;a, as the 

 region is characterised by ancient life. 



The author then deals similarly with the distribu- 

 tion of iMesozoic and Palaozoic life, and the former 

 continental unions thus proved. He quotes widely 

 from literature, and numerous references show his 

 indebtedness to the works of Lydekker. 



The second main division of the work is geological, 

 and here the author is largely dependent upon the 

 work of Suess. He summarises the evidence from 

 the various former continents, including North Atlan- 

 tis, South Atlantis, Angaraland, Gondwanaland, the 

 larger Oceania and Antarctica. He then describes the 

 seven chief Archaean massifs, the ancient coigns of 

 the earth, which have remained unbroken since the 

 earliest geological times, and have guided the course 

 of the earth-folds that formed the chief fold-mountain 

 lines of the earth. 



The section on historical geology summarises the 

 \ chief geographical incidents and the characters of the 

 life of each of the geological systems, and insists on 

 the periodicity in the dominant phenomena. The 

 author's conclusions, though . probably right in the 

 main, perhaps overstate the regularity of the 

 periodicity. For instance, he divides known geological 

 history into six cycles — the Cainozoic-Mesozoic, 

 Upper Palaeozoic, Middle Palaeozoic (Lower Devonian 

 and Silurian), Lower Palseozoic (Ordovician and Cam- 

 brian — the author, however, does not adopt the former 

 term), the .^Igonkian, and the Urschiefer. Each cycle 

 he represents as beginning with a marine transgres- 

 NO. 202 1, VOL. 78] 



sion, followed by a period of fold-mountain formation, 

 and then by vast eruptions of basic volcanic rocks, and 

 each cycle closes with a Glacial period. He accepts 

 six Glacial ages, viz. one in the lower and one at 

 the top of the Algonkian, and others in the Upper 

 Ordovician, Lower Devonian, Permian, and Pleisto- 

 cene. The evidence for these six glaciations is not yet 

 convincing. 



Dr. Arlt traces, too, in the last pages of his work 

 the influence of the former land distribution 

 on the distribution of human races. He assigns 

 the original home of mankind to the area 

 north of the Himalaya. .\s land distribution 

 at the arrival of man was in broad outlines essen- 

 tially the same as now, the migrations of man, as is 

 shown in the last of Dr. Arlt's admirable series of 

 charts, followed the existing land lines. The woolly- 

 haired races spread from Southern Asia into Africa 

 and Melanesia; the stiff-haired Malays crossed over- 

 sea from Malaysia to Madagascar and the islands of 

 the Western Pacific (the author unfortunately includes 

 the Maoris as Malays), and the allied Mongols occu- 

 pied northern Eurasia and America. The members of 

 the author's last group, including the Indo-Germanic, 

 Semitic and Hamitic peoples, and Dravidians, 

 Veddas and Australians, overran southern Europe 

 and northern .Africa, while one seciion of it passed 

 through the Malay Archipelago to .\ustralia. 



Dr. Arlt's work is extensive, comprehensive— the 

 index occupies ninety-eight pages— and ambitious. 

 Probably not one of his readers will agree with it all. 

 The chapters are necessarily of unequal value. Among 

 his classifications of animals, e.g., that of the Echino- 

 derms on his phylogenetic chart of that group, he 

 adopts a now out-of-date system from von Zittel's text- 

 book of 1S83. But the work is of great value; it is 

 original, suggestive, and, taken as a whole, we think 

 sound. It is the fullest statement yet issued of the 

 doctrines of a school of geological thought which 

 appears to be making steady progress, and it shows 

 the necessity for the combined study of palaeontology, 

 geology, and petrography in discovery of the actual 

 history of the geography of our earth. 



J. W. Gregory. 



BOTiATY O-^ THE VOY.iGE OF THE 

 " VALDIVIA." 



Wissenschnftliche Ergcbnisse der deiitschen Tiefsee- 

 Expcdition attf dern Dampjcr " Valdivia." 1898-1899. 

 Edited by Prof. C. Chun. Vol. ii.. Part i.. No. 2, 

 BeitrJige zur Kenntniss der Vegetation der 

 Canarischen Inseln. By H. Schenck. Pp. 180; with 

 12 plates. Price 45 marks. Vol. ii.. Part ii.. No. 3. 

 Das Indische Phytoplankton. By G. Karsten. 

 Pp. 326 ; with 25 plates. Price 70 marks. (Jena : 

 Gustav Fischer, 1907.) 



THE second volume of these memoirs has been 

 assigned to the botanical results of the X'aldivia 

 expedition. The first part deals with insular floras, 

 the second with marine floras, and there will be an 

 account of plants collected in countries visited on the 



I 



