144 FIELD GEOLOGY. 



but that this depth was not very great, is evidenced by 

 their muddy and shaly character, caused by the admix- 

 ture of sediment brought down from higher land. A 

 reverse movement soon set in, the area slowly rose 

 again and the shales with ironstone nodules were ac- 

 cumulated ; finally, the bay or estuary must have been 

 silted up by the deposition of such sediment and again 

 became a land surface at the time when the plants 

 forming the uppermost coal-seam grew and nourished in 

 their rank luxuriance. 



CHAPTER III. 



Preservation, Naming, and Arrangement of Fossils Value of 

 Palaeontological Evidence Evidence of Physical Conditions. 



Preservation of Fossils. Having collected and brought 

 away our fossils in the manner described in the preced- 

 ing pages, it behoves us to say a few words regarding 

 their further treatment and mode of preservation. 



We have already recommended that a note of the 

 locality and the bed from which they were obtained 

 should be written on the paper or box in which they 

 are enclosed, and if this is done at the time, they may 

 be deposited at headquarters and left till winter or 

 wet weather affords leisure for dealing with them. 



They should then be taken out, carefully inspected 

 and sorted, only the very worthless duplicates from the 

 same bed and place being put on one side ; attention 

 must then be paid to the more delicate specimens, such 

 as those obtained from the loam-pit in fig. 8, from Crag- 

 sands or from River-gravels ; these will require thorough 



