j68 



NATURE 



[July iS, 1S95 



ting no criterion of geological age in the nomenclature of 

 the rocks. 



Throughout the book, each rock group is treated for 

 the most part under the three headings : constituent 

 minerals, structure, illustrative examples. Under the 

 last heading, purely petrographical descriptions are given 

 of typical examples, chosen generally from British rocks. 



The sedimentary rocks are treated under the divisions, 

 arenaceous, argillaceous, calcareous, and pyroclastic. In 

 perhaps no other English text-book have the microscopic 

 characters of the sedimentary rocks been so minutely 

 described. The subject of metamorphism is treated 

 under the two heads of thermal metamorphism and 

 dynamic metamorphism, and the effects produced on 

 arenaceous, calcareous, argillaceous and igneous rocks 

 are separately described. The book concludes with a 

 short chapter on various crystalline rocks, including 

 gneisses, granulites, &c. It is, perhaps, almost inevit- 

 able, owing to the nature of the subject, that the book 

 should give the general impression of consisting of a 

 series of descriptions of rock-sections ; but, be this as it 

 may, there can be nothing but praise for the clear and 

 straightforward way in which the author has presented 

 his facts, and for the wealth of new matter which the 

 book contains. The book shows evidence of most careful 

 research into the literature of the subject, and is in 

 fact thoroughly up to date, containing many extracts 

 from papers which have appeared within the present 

 year. G. T. P. 



OUR BOOK SHELF. 

 Garden Flowosand Plants: a Primer for Amateurs. 



By J. Wright. With fifty Illustrations. (London : 



.Marmillan and Co., 1895.) 

 One of the great advantages of gardening and of a love 

 of flowers consists in the fact that they may be indulged 

 in by rich and poor alike. 



The rich have no monopoly in the beauty of flowers, 

 the poor are not debarred from their enjoyment. The 

 costliest orchid in a ducal garden is not one whit more 

 beautiful than an Iris which may be bought for a few pence. 

 If a slug devour the one it is easily replaced, if such an 

 accident befall the other the loss may be beyond repair. 

 Nor by those who look beneath the surface and seek to 

 |jenetrate the significance of the diversity of form, and 

 the meaning of the beauty they witness, is costly 

 expenditure needed. The cheapest and commonest 

 afiord as copious materials for research and inves- 

 tigation as the dearest plant in the nurseryman's price 

 list. Anything that will lighten the sordid conditions 

 under which so many of the poorer classes live, anything 

 that will brighten their homes and give them an interest 

 in something beyond their daily toil, must be considered 

 as a l>oon of incalculable value. .Such a boon is offered 

 by the pursuit of gardening. In country districts, more- 

 over, where small gardens and allotments can be had, 

 gardening may be made to add considerably to the 

 resources of the family. It may be doubtful whether 

 market-gardening on a large scale will always be profit- 

 able, but there can be no doubt that the small plot of the 

 lalx)urcr may he turned to gowl account, provided 

 circumstances are even only moderately favourable. To 

 provide for the needs of small gardeners and amateurs, 

 .Mr. Wright has published the little manual before us. 

 The author is an accomplished practitioner, and his ex- 

 perience as a County Council lecturer has enabled him to 

 ascertain precisely what is wanted by his auditory. Mr. 

 Wright Ixrgins at the beginning by telling his readers how 



NO. 1342, VOL. 52] 



to make a yarden, how to lay down gra\el walks, what to 

 grow on walls, what on beds, even what may be cultivated 

 in areas. The principal categories of hardy plants are 

 passed in review, such as annuals, perennials, bulbous 

 plants, bedding plants, and so on, and clear directions are 

 given as to their management from beginning to end. In 

 all this there is not much that needs comment from a 

 reviewer, who can only say that the little primer is well 

 done, and excellently suited for its purpose. 



An explanation of the real cause of " damping " off 

 would ha\ e been of value, as the most " practical " of 

 gardeners is not desirous of cultivating fungus at the 

 expense of cherished seedlings. 



The small illustrations are helpful, and a full index 

 adds materially to the value of the book. 



T/ie Time Machine. By H. G. Wells. (London: Wm 



Heinemann, 1895.) 

 iNGEXlorsi.v arguing that time may be regarded as the 

 fourth dimension of which our faculties fail to give us any 

 distinct impression, the author of this admirably-told 

 story has conceived the idea of a machine which shall 

 convey the traveller cither backwards or forwards in time. 

 -Apart from its merits as a clever piece of imagination, 

 the story is well worth the attention of the scientific 

 readef, for the reason that it is based so far as possible on 

 scientific data, and while not taking it too seriously, it 

 helps one to get a connected idea of the possible results 

 of the ever-continuing processes of evolution. Cosmical 

 evolution, it may be remarked, is in some degree subject 

 to mathematical investigations, and the author appears to 

 be well acquainted with the results which have been ob- 

 tained in this direction. It is naturally in the domain of 

 social and organic evolution that the imagination finds 

 its greatest scope. 



Mounted on a "time-machine" the " time-tra\cller' 

 does not come to a halt until the year eight hundred 

 and two thousand, and we are then favoured with his- 

 personal observations in that distant period. In that 

 " golden age," the constellations had put on new forms, and 

 the sun's heat was greater, perhaps in consequence 

 of the fall of a planet into the sun, in accordance with 

 the theory of tidal evolution. " Horses, cattle, sheep, and 

 dogs had followed the ichthyosaurus into extinction " ; but, 

 most remarkable of all, " man had not remained one 

 species, but had difl'crcnliatcd into two distinct animals," 

 an upper-world people of " feeble preltiness," and a most 

 repulsive subterranean race reduced to mere mechanical 

 industry. It is with the time-tra\ eller's adventures among 

 these people, and their relations to each other, that the 

 chief interest of the story, as such, belongs. 



Continuing his journey to an age millions of years hence, 

 nearly all traces of life had vanished, the sun glowed 

 only with a dull red heat, tidal evolution had broufjht 

 the earth to present a consl^int face to the sun, and the 

 sun itself covered a tenth part of the heavens. These and 

 other phenomena are very graphically described, and 

 from first to last the narrative never lapses into dulness. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither <an he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taien of anonymous communications. ] 



The Teachinj; University for London. 



I liAVi. read with surjinso your article cjn the Uiiivcrsily of 

 Loiulon. 



rrolahly by some accident you had not seen my reply to 

 I..ord Kelvin's letter when you went to press. I now enclose a 

 copy, and trust to your fairness to insert it : 



" 2 St. fames' s S,/uare, S. IV., fuly 9. 



" Mv Ukar RiJi'KKR,— I am sorry I could not inimcdialcly 

 answer the letter which you have forwarded t'l me on behalf of 



