26o 



NATURE 



[Jan. 1 8, 1877 



creep fuither and further north, whilst the descendants 

 of cold-loving plants would retreat from the advancing 

 temperature. Vice versa, whenever the area became gra- 

 dually colder, the heat-loving plants would, from one 

 generation to another, retreat further and further south, 

 whilst the cold-loving plants would return to the area from 

 which their ancestors had been driven out. In each case 

 there would be some lingering remnants of the retreating 

 vegetation (though perhaps existing with diminished 

 vigour), growing alongside of the earliest arrivals of the 

 incoming vegetation. Such is a possible explanation of 

 our finding these plant remains comingled together. It 

 must, too, be borne in mind that it is not so much the 

 mean temperature of a whole year which affects the possi- 

 bility of plants growing in any locality, as the fact of what 

 are the extremes of summer and winter temperature. For 

 example, one place may have a mean winter temperature 

 of 50°, and a summer one of 70°; while another place 

 might have a mean winter temperature of 20°, and a 

 sumnrer one of 100°, and yet both have a mean annual 

 temperature of 60°. In Cornwall the maiden- hair fern 

 grows in sheltered localities, because the winter tempt ra- 



V\Q. 5.- GrOUI" tF MONOCOTVLEDONe, FROM THE LoWER BAGSHOT BeDS. 



I, Fan Palm ; 2, Smilax ; 3, Feather Palm. 



ture never sinks to the point that would cause its de- 

 struction. Again, at that most charming spot in the west 

 of Ireland, Glengariff, the arbutus still forms an abundant 

 underwood ; and the Irish filmy fern flourished in many 

 favoured spots until quite recently, when the modern, too 

 comfortable Eccles Hotel has retained tourists in the 

 district, who have luthlessly carried off, as reminiscences 

 of a pleasant holiday, this which was one of the most 

 attractive features to the botanists. 



These facts, which seem so simple when laid out in 

 diagrams, are the results of long-continued and careful 

 work; but you may take my word for it, having enjoyed the 

 pleasure during my holidays for many summers, that 

 hunting for fossils is a fine, healthy and active exercise. 

 As regards this particular district, let me tell you some of 

 my operiences. Fossils are not to be obtained here 

 without hard work ; the steep and crumbling cliffs have 

 to be climbed, and most diligent search has to be made 

 for indications of them. Fifty times, perhaps, the cliff 

 may be laboriously scaled to examine what appears from 

 the beach to be a promising-looking patch of clay, to 



result only in disappointment ; either the clay turns out 

 to be too sandy, and the impressions valueless ; or it con- 

 tains nothing ; or it is found, on nearing it, to be in- 

 accessible. But supposing well-preserved leaf-impressions 

 reward the search, a secure footing has first to be cut with 

 a light pickaxe ; then the sands or clays overlying the 

 leaf-bed have to be removed by spade and pick — real 

 navvy's work this — then to get out blocks large enough 

 to contain the palm-leaf shown in this drawing, which is 

 only enlarged twice, the leaf-bed has to be undermined 

 to a depth of five or six feet, a difficult operation requiring 

 patience, and the then hanging mass of clay has to be cut 

 off with the pick, beirg too plastic to break away by its 

 own weight. When nearly cut through, it gradually breaks 

 away, and falls gently on to the platform prepared for it 

 underneath. The blocks thus obtained are sometimes too 

 large for three or four men to tilt over. The method is 

 then to leave them to dry, as when wet the clay will not 

 split to disclose the leaves. It is then, I can assure you, 

 that I esteem myself fortunate if some too curious excur- 

 sionist, or enthusiastic townsman, does not arrive during 

 my absence with a hammer to break the blocks up. So 

 great has been the curiosity excited, that fossilizers have 

 so far forgotten their sense of justice as to get up at day- 

 break to appropriate the result of my work had not the 

 faithful coast-guardsmen, with a keener sense of justice, 

 been near. 



Wet weather of course puts a stop to operations, and 

 buries the working in mud and sand, sometimes two or three 

 feet deep even in a single night. When the workings are 

 as far off from your headquarters as at Poole Harbour, and 

 the specimens heavy, a boat is necessary to convey them 

 home. The most enjoyable moments are, perhaps, those 

 occupied in splitting the blocks, as one then shares what 

 I should suppose to be the excitement of gold-workers, 

 except that gold-finding must be more monotonous, as in 

 this case no one can say what sort of treasure may reward 

 us next. Anyhow, it is a recreation strongly to be recom- 

 mended to those who like healthy exercise, freedom, and 

 the sea. 



[A large and heavy block of matrix was then split, in 

 illustration of this part of the lecture, and a layer showing 

 hundreds of leaves, exposed for the first time to view.] 



I have now endeavoured to give you as accurately 

 as I can, the absolute facts as far as we can learn 

 them, respecting the conditions under which these beds • 

 were deposited, the sources from which the material 

 was derived, and so far as we can tell, by comparison 

 with existing vegetation, what were the trees of which 

 these leaves are the records, and also the climatal con- 

 ditions under which they grew. We may now, in con- 

 clusion, allow our imagination to come into play, a scien- 

 tific use of the imagination, I hope it is, while we picture 

 to ourselves the appearance of this area during the time 

 these beds were being formed. The changing force of the 

 streams and their directions varjing from time to time, 

 would, as we have already said, frequently undo the work 

 of accumulation which had been previously done. 



We have reason to believe that there was here a width 

 of valley closed in to the north by the chalk hills which 

 are still represented by the chalk range of North Hamp- 

 shire and Wiltshire, and on the south and east by accu- 

 mulations forming the lagoon barrier of which I have 

 spoken. The course of the stream was from west to east. 

 To the east was the sea, to the west was the valley of the 

 stream, about some of the conditions of which we are 

 necessarily uncertain, in consequence of the changes from 

 upheaval and denudation, which have extensively modified 

 that district. When the streams were from the rainy 

 seasons swollen they moved along at a rapid rate, sweep- 

 ing away previously deposited beds and also bringing i 

 down coarse quartz grit and blocks, which formed the 

 gritty beds of which I have spoken. When the streams 

 were not so violent then there were doubtless frequently 



