ss 



NOTES ON THE SPECIMENS 



OF WHICH 



PHOTOGRAPHS APPEAR ON 

 THE PRECEDING PAGES . . 



BY 



E. A. NEWELL ARBER, M.A., F.L.S., F.G.S., 



Demonstrator in Paleobotany in the University 

 of Cambridge. 



The fossil plants figured in this little book are all from the very 

 ancient rocks, known to Geologists as the Coal Measures or Upper 

 Carboniferous, which form the great coal-bearing strata in Britain. 

 Most of them are common species to be collected by hammering 

 and splitting the shales and sandstones thrown out of the mines on 

 to the waste heaps of collieries in various parts of this country. 



The age of these specimens is inconceivably great. If it could be 

 guessed at, it would amount to millions of years. It is therefore 

 very wonderful that they should be so well preserved. 



A word or two about the manner of preservation may not be 

 out of place here. Fossil plants nearly always occur in small 

 fragments — a leaf here, a stem there, and a cone or a seed some- 

 where else. It is rarely'' that two part.s of the same plant are to be 

 found still united, though not infrequently the leaves are still 

 attached to the stems. 



No part of the original substance of the plant remains in any 

 specimen. But replicas of them have been handed down to us, and 

 these have been formed in two quite diflerent ways, as follows : — 



Casts and Impressions. — When one of these ancient plants 

 died, one or other pan of it, let us say the stem, was washed away 

 by a stream, and became incrusted or covered up in sand or mad. 

 When the sand or mud hardened and became converted irito a 

 sandstone or shale, the layer which snrrounded the stem in question 

 took an impression of its exiernal features, just as wax takes an 

 impression of a seal, but with this difference, that the impression 

 of the sandstone was the reverse of the stem, prominences becoming 

 hollows and vice-versa^ whereas with a seal, which is purposely 

 made as a reverse, we get a positive impression on the wax. 



Next the stem itself slowly decayed away altogether, or was 

 converted into a very thin layer of coal forming a film over tlie 

 sandstone or shale impression. When this process was complete 

 an empty space of a size corresponding to that of the ^tein was 

 left. This space may again have become fdled with mud or sand, 

 in which case we get a cast^ fitting into the impression already 

 made. The features of the cast correspond exactly to those of the 

 original stem. 



