TRANSACTIOKS OF SECTION K. 827 



of the earth, with its embedded remains, must not be looked at as a well-filled 

 museum, but as a poor collection made at hazard and at rare intervals.' 



As a preliminary consideration, we must decide upon the most convenieut 

 means of expressin-f the facts of geographical distribution in a concise form. Tbe 

 recDgnised botanical regions of the world do nfit serve our purpose ; we are not 

 concerned with the present position of mountain-chains or wide-stretcbing plains 

 that constitute natural boundaries between one existing flora and another, but 

 simply with tbe relative geographical position of localities from which records of 

 ancient Horas have been obtained. In the accompanying map I have divided the 

 surface of the earth into six belts, from west to east. Tlie most northerly or 

 Arctic Belt includes the existing land-areas as far south as latitude 60°, com- 

 prising— 1, Northern Canada; 1', Greenland and Iceland; ."'., Northern Europe; 

 4, Bear Island and Spitzbergeu ; 5, Franz Josef's Land ; 6, Northern Asia. The 

 North Temperate Belt, extending from latitude 60'^ to 40°, includes— 7, South 

 Canada and the northern United States; 8, Central and Southern Europe; U. 

 Central Asia. The North Sub-tropical Belt comprises the land between latitude 40° 

 and the Tropic of Cancer, including— 10, the Southern States of North America ; 

 11, Northern Africa, part of Arabia and Persia; 12, Thibet and part of China; 

 13, Japan. The Tropical Belt, embracing the laud-areas between the Tropics of 

 Cancer and Capricorn, includes- 14, Central America and the northern part of 

 South America ; 15, Central Africa and Madagascar ; 16, India, the Malay 

 Archipelago, and Northern Australia. The South Sub-tropical Belt, extending 

 from the Tropic of Capricorn to latitude 40° south, includes— 17, Central South 

 America; IS, South Africa; 19, Central and Southern Australia. The South 

 Temperate Belt includes — 20, the extreme south of South America; 21, Tas- 

 mania ; 22, New Zealand. 



Pre-Devonian Floras. 



The scanty records from pre-Devonian rocks afl'ord but little information as to 

 the nature of the vegetation that existed during the period in which were 

 deposited the Cambrian, Ordovician, and Silurian strata that now form the 

 greater portion of the Welsh and Cumberland hills. We must wait for further 

 discoveries before attempting to give more than the barest outline of the plant- 

 life of these remote epochs. Our knowledge of the plant-world which existed 

 during the Silurian period is far too meagre to justify any statement as to geogra- 

 phical distribution. Of the few records of supposed Silurian plants, several have 

 been shown to be unsatisfactory, and the nature of others is too uncertain to admit 

 of accurate identification. The Lepidodendron-like fossil from the Clinton lime- 

 stone of Silurian age in Ohio, described by Clay pole in 1878 as Glyptodendron, has 

 been referred by a later Avriter to a Cephalopod! Stur's Bohemian plants, described 

 in 1881, are too imperfect to atlbrd any information of botanical value •, while the 

 ferns and lepidodendroid plants recently recorded by Potonie from the Ilartz 

 Mountains are more likely to be of Devonian than Silurian age. 



The genus Nematophycus, originally described by Dawson as Protota.iites, and 

 afterwards referred by Carrutbers to the Algre, constitutes the most satisfactory 

 example of a Silurian plant. This genus, which has fortunately been preserved 

 in such a manner as to admit of minute microscopical examination, represents a 

 widely spread algal type in Silurian and Devonian seas. It has been found in 

 Silurian strata in Wales, Shropshire, and New Brunswick ; also in Devonian 

 rocks of Eastern Canada, New York, Ohio, and North-A^^est Germany. The 

 tubular elements composing the stems of some species of Nemafojihycus — which 

 reached a diameter of 2 or ■] feet — exhibit a regular variation in width, giving 

 the appearance of concentric rings of growth, as in tbe stems of the tree- 

 like Zessonia, an existing genus of Antarctic seaweeds. This structural teature 

 presents an impressive image in stone of a plant's rhythmical response to some 

 periodically recurring conditions of growth in the waters of Palaeozoic seas. 



