136 FIELD GEOLOGY. 



and should be immediately packed in boxes with wool or 

 bran. 



Note. Where these materials are unattainable, 

 or have been forgotten, clean sand from the shore 

 or pit itself may be used as a fair substitute, though 

 it has, of course, the disadvantage of being much 

 heavier. 



Ordinary chip-boxes have already been mentioned as 

 useful for this purpose, and are easily stowed and car- 

 ried, but they are sometimes hardly strong enough, and: 

 such small wooden cases as those in which baking- 

 powder is sometimes sold will be found serviceable. 



We have hitherto spoken of the fossil remains which 

 are actually included in the matrix of the bed or stratum, 

 and were deposited there in most cases after the death 

 of the animal, and during the accumulation or deposition 

 of the materials which form the matrix. But since 

 every bed or layer of a sedimentary rock once formed 

 the bottom of a river, lake, or sea, we should naturally 

 expect to find some fossils resting on their surface more 

 or less in the position of growth, as well as the tracks or 

 marks of animals which also come under the category 

 of fossils. These, of course, will be seen by separating 

 the layers which compose the series of strata under 

 examination, or may be found on the surface of beds 

 already exposed. The Dudley slabs are good examples 

 of this, and other instances are often found in the shales 

 and limestones of the Oolitic series. 



Nodule beds, bone beds, and layers of flint or chert 

 all also mark pauses in deposition of greater or less 

 length, and are often very rich in organic remains. In- 

 deed, the nodular concretionary masses which usually 

 characterize such beds owe their origin mainly to the- 



