May 12, 1921] 



NATURE 



347 



(Bureau of Forestry, Government of Formosa), Bunzo 

 Havata continues his descriptive account of the flora 

 of this island. The volume contains studies of genera 

 of a large number of families of flowering plants, and 

 includes descriptions of 139 new species ; the arrange- 

 ment follows the system of Benthafh and Hooker's 

 "Genera Plantarum." The descriptions (in Latin) are 

 full and clear, and the volume is remarkably well 

 illustrated with text-figures and plates. Two new 

 genera are established, one, Dolichovigna, a climbing 

 bean near Phaseolus and Vigna ; the other, Pseudo- 

 smilax, a member of the family Liliaceae, and inter- 

 mediate between Smilax and Heterosmilax. Nine 

 genera are also recorded as new to the flora of the 

 island, which so far as is at present known includes 

 3608 species of flowering plants representing 1185 

 genera and i6g families. 



In the Journal of Ecology (vol. viii.. No. i) Miss 

 L. S. Gibbs gives an account of the phytogeography 

 and flora of the mountain-summit plateaux of Tas- 

 mania based on her own observations and collections. 

 The vegetation of the island may be divided into three 

 principal plant formations : (i) The austral-montane 

 flora of the mountain-summit plateaux, which repre- 

 sent the remains of the huge lava plateau of which 

 the island formerly consisted. The major and most 

 interesting portion of the endemic flora is entirely 

 limited to these summit plateaux; one of the peculiar 

 features is the almost complete absence of herbaceous 

 plants. (2) The mixed forest of the west coast, not 

 very rich in species and characterised more by dense- 

 ness of growth than by height. There is a marked 



endemic element in this flora which probably originated 

 on the higher lands. (3) Eucalyptus formation, 

 occupying the greater part of the island, consisting 

 mainly of secondary open forest, and purely Australian 

 in type, A description is given of the various portions 

 of isolated tableland which form the mountains of the 

 island and at no point exceed 5000 ft., and the writer 

 describes the chief plant-associations, enumerating 

 the plants which she collected in each. On the most 

 exposed and highest levels a mosaic of small moss-like 

 plants is developed, with .inconspicuous flowers, form- 

 ing a hard, even surface. This is succeeded by a 

 mountain shrubbery, the dominant association of the 

 more exposed portions of the plateau summits. Lower 

 come forest-associations in succession, namely, dwarf 

 mountain forest, low mountain forest, and Eucalvptus 

 scrub. In conclusion, the author refers to the marked 

 relation between the mountain flora of North-West 

 New Guinea, the subject of a former paper, and the 

 so-called "Antarctic flora" of the southern hemi- 

 sphere. Recent work on meteorological conditions 

 provides an explanation of this relation, namely, in 

 the persistent north-west wind of high altitude over 

 the mountains of New Guinea and across the Aus- 

 tralian continent. Seeds transported by this agency 

 would be precipitated in southern latitudes, where 

 they remain within the radius of the persistent 

 westerly winds and gales of the Antarctic seas. 



A systematic enumeration is given of the species 

 collected on the mountain-summit plateaux and in 

 the mixed forest from September, 1914, to March, 

 1915- 



Origin of Petroleum and Cause of Gas Pressure.^ 



THE important volume referred to below is 

 bountifully illustrated with photographs, sec- 

 tions, and maps, and gives a comprehensive account 

 of some 150 square miles in the midst of the Cali- 

 fornian oilfields, a territory which provides nearly 

 half the oil which the State produces, and includes 

 its greatest oilfield. Here, too, is the famous " Lake- 

 view Gusher," which yielded 8,000,000 barrels of oil 

 in eighteen months. The area has been discussed 

 previously both by State and Federal geologists, 

 notably some ten years ago by R. Arnold, H. Johnson, 

 and R. Anderson in Bulletins 406 and 471, but since 

 that time there has been much further development, 

 and many new facts are available. 



The work contains a wealth of information which 

 is rendered easily accessible by its systematic arrange- 

 ment and clear table of contents. The book com- 

 mences with a brief "Summary of Results," which is 

 followed by an informative bibliography. " Strati- 

 graphy," which occupies 34 pages, is dealt with under 

 the headings of the various formations. Then follow 

 "Structure" (pp. 54-63) and "Petroleum " (pp. 63-87), 

 whilst a detailed description of the " Productive Field" 

 occupies the latter half of the book. In the pocket 

 at the back of the volume is a geologic map of the 

 region and large-scale topographic and structure 

 maps of the oilfield, together with many sections 

 across the productive area. 



The main scientific inferences difi'er little from 

 those set forth in the earlier bulletins. It is made 

 clear that the petroleum was generated within the 

 Tertiary deposits, which are at least 18,000 ft. in 

 thickness, ranging from Eocene to Pliocene. Regard- 



i United States Geological Survey, Professional Paper No. ii6: "The 

 Sunset Midway Oil Fie'd of California.' Part i., "Geology and Oil 

 Resources. " By R. W. Pack. Pp. 179. 



NO. 2689, VOL. 107] 



ing the origin of the oil, the author's e.xplanation is 

 that previously formulated by .'\rnold and Anderson; 

 but he does not ascribe the source of the carbon 

 wholly to the diatoms and foraminifera. "The 

 petroleum has originated in the diatomaceous shale 

 formations, chiefly from the alternation of organic 

 matter contained in diatoms and foraminifers, but 

 probably in part also from the alteration of terrestrial 

 vegetal debris." Later "the oil has collected in part 

 in sandy beds that are intercalated with the [diatom- 

 aceous] shale, but chiefly in the porous beds of younger 

 formations that rest unconformably upon the shale." 

 With reference to migration and accumulation, the 

 author affirms that much of the oil in the pools " has 

 migrated from the beds beneath the San Joaquin 

 Valley to the foothills and collected in the small anti- 

 clines that extend from the hills out into the valley." 

 The reservoirs of oil are now chieflv in the later 

 Tertiary " [Miocene or Pliocene] sandy' beds that rest 

 unconformably upon the diatomaceous shale." 

 _ Some interesting matters are discussed in connec- 

 tion with the gas pressure and concerning chemical 

 reactions on the. petroleum within the oilsands. The 

 pressure in these fields is not proportionate to depth, 

 and usually is considerablv in excess of the theoretical 

 "hydrostatic pressure." The author holds that the 

 oil, whilst within the reservoirs, has been affected by 

 chemical reactions with minerals. In particular, 

 oxidation by sulphate-laden waters has produced a 

 marginal ring of heavy tar around the pool where its 

 bottom rests upon the under-water. This tar seals 

 the oil pool within a definite space, and any further 

 quantities of gas generated from the oil can be 

 accommodated only by increase of pressure. Such 

 conditions probably account for the great gusher- 

 wells of this region. T. O. B. 



