Jan. 1 8, 1877] 



NA TURE 



259 



there are more. In some, these principal ribs are very 

 stronp, and form prominent features ; in others, as in the 

 convolvulus, they are but slight. Some of these secondary 

 ribs run straij^ht to the margin, and in other cases they are 

 curved. Again, in some they run right out to the extremity 

 of the margin, as in the elm ; and in others they are curved 

 back, as in the fig. These are things to be noticed, which 

 it will be seen are of consequence. 



I wish now to refer to the character of the margins of 

 the leaves. Here is a drawing of a fig leaf in which a per- 

 fectly smooth margin will be observed ; whilst the elm is 

 saw-like, or serrated, as botanists call it. In the dryandra 

 the margin is deeply notched, whilst in a strange-looking 

 form (Stenocarpus) the edge is markedly lobed ; in the 

 case of some palmate leaves the edge is smooth, as in the 

 passion-flower, or serrated, as in the fossil aralia. Those 

 who have paid any attention to leaf form, have no 

 doubt observed that leaves, even from the same plant, 

 differ in some of these characters. This constitutes one 

 of the greatest difficulties which presents itself to the 

 botanist, in the endeavour to decide by comparisons to 

 what plants the fossil remains probably belonged. Still, 

 there are numbers of specimens with which we have to 

 deal presenting forms so unmistakably alike that we are 

 able to group them together ; and even putting on one 

 side many fossil forms about which we must feel consider- 

 able hesitation, there still remain a vast number about 

 which we can feel little hesitation as to the value of the 

 comparisons. 



It is worth while to point out that when we compare 

 these leaves with the existing flora and contrast in like 

 manner the plants of the coal period with the existing 

 vegetation, we see that there is a much closer resem- 

 blance between these plants and the present plants than 

 there is in the case of coal plants. That is, that in these 

 forms we have a nearer approach to the existing state of 

 things than there was in the coal period, a matter which, 

 in viewing the evolution of plant life, cannot be over- 

 looked, whatever may be the value to be set on such 

 evidence. Those who know anything of the plants of the 

 coal period are aware that we find there gigantic forms of 

 which we have only dwarf representatives at the present 

 time. The principal of these forms are gigantic horse- 

 tails or Equisitaceae, great lycopods, as the Lepido- 

 dendron and Sigillaria, and tree-ferns, all very unlike the 

 representatives of these groups now living. Here, how- 

 ever, the resemblances to the existing vegetation is close, 

 not only in the arrangement of the ribs, but the size of the 

 leaves, and also in those cases where we have groups of 

 leaves joined by twigs, the method of attachment is 

 similar. 



To determine to what kind of plants each of these 

 leaves belongs is a matter of considerable difficulty and 

 requires an extensive knowledge of the plants now living 

 on the earth. Although we have collections of growing 

 plants from different parts of the world in various con- 

 servatories, such as at Kew, it is on the dried specimens 

 brought home by travellers, or sent from abroad, that we 

 mainly have to depend. How frequently leaves closely 

 resembling each other but belonging to plants of widely 

 different kinds are met with, the careful student of botany 

 knows well. It requires a comparison by a skilled eye of 

 the most minute details to arrive at conclusions on which 

 any reliance may be placed. 



The work of comparison of this immense number of 

 leaves is necessarily a work of considerable time, and is 

 still in progress, but some conclusions have already been 

 arrived at. I call your attention to a large group of 

 growing plants, from the conservatory of Mrs. J. E. 

 Gardner, which illustrate the kind of foliage existing 

 in England in the Eocene time. Those who have 

 paid attention to this subject will not doubt that these 

 are palms ; these are unmistakable ferns ; botanists are 

 agreed that this form is xmdoubtedly referable to the 



group to which this dryandra belongs ; this may with 

 almost cettainty be referred to the beech tribe ; this 

 doubtless belongs to the same tribe as the pea ; this 

 is an aralia ; this an acer or maple ; this a laurel, and 

 this a yew. Specimens of elm, acacia, chestnut, great 

 aroids, as well as hundreds of other forms, have been ob- 

 tained, some of the comparisonsof which have already been 

 determined, and some few are of forms which appear to 

 have no living analogies whatever. There are also count- , 

 less fruits, many of which can be recognised as like those.^ 

 now existing ; a few flowers too have been met with. 

 These fruits are of great assistance in telling us what 

 plants were living at the time, as they are compared with 

 greater certainty than the leaves can be. 



I have mentioned the cabinets in the Loan Collec- 

 tion ; close by is a cabinet which contains the collection 

 made by Baron von Ettingshausen, and although time 

 does not permit me to do more than allude to them, I 

 would just mention that collections of an approximately 

 similar geological age have been made from Switzerland, 

 Italy, Greenland, and Austria, so that taking together all 

 these localities we get a fair notion of what was the vege- 

 tation of the period which geologists call Eocene. You 

 must remember geology is a study only of this century. 

 Interest, at first small, spreads now over all Europe, and 

 gradually records of past vegetations of different ages are 

 being brought to light and compared. 



I would say a word or two by way of explanation of 

 the origin of the different colours of the sands and clays 

 which have been mentioned. The yellows, buffs, and reds, 

 which form the prevailing colours of the lower series, owe 

 their origin to iron in various chemical conditions. The 

 granite from which they were derived contains sufficient 

 iron to account for iron being in solution in the streams 

 by which they were deposited. The different colours of 

 the different oxides of iron are here shown. The anhydrous 

 sesquioxide is of a deep tinge : the hydrous sesquioxide 

 gives a yellow colour. [A successful experiment was 

 then made with a large glass jar of rain-water with dis- 

 solved grey granite held iti suspension. To show the 

 amount of iron present in the granite, a little ammonia 

 was added, which changed it to a dark colour. The 

 green oxide thus obtained would, on evaporation of the 

 water, take another degree of oxygen and change to a 

 bright red sesquioxide. This red oxide was produced in 

 a second jar, and shown to be the same as the colouring 

 matter of the red clays] De la Beche, in his researches in 

 theoretical geology, alludes to the fact that pipe-clays of 

 similar colours are now being deposited in some of the 

 lakes of North America. 



Whilst some of the dark colouring of the darker clays is 

 due to iron, that of some of the middle clays may be due 

 to the fact that, whilst these beds were being deposited, 

 the source of the stream was coming from a district 

 farther north, cutting perhaps across the Somersetshire 

 and Gloucestershire coal-field. 



The question may perhaps have presented itself to your 

 minds — how is it possible that the tropical forms of which 

 we have spoken, such as the palm, aroids, cactus, &c., 

 could have grown alongside of the apparently temperate 

 forms, such as the oak, elm, beech, and others. Time 

 does not allow that I should go at any length into the 

 explanation of this ; but I may just remind you that in 

 the long geological record of the beds found in England, 

 there are to the geologist unmistakable indications of 

 many changes in climate. Further, astronomers, having 

 calculated the path of the revolution of the earth in ages 

 past, tell us that in successive periods, each consisting of 

 about 26,000 years, each hemisphere, northern and south- 

 ern, has been successively subject to repeated cyclical 

 changes in temperature. There have been for the area 

 which is now England many alternations of long periods 

 of heat and cold. Whenever the area became warmer, 

 the descendants of semi-tropical forms would gradually 



