52 INVERTEBRATE PALAEONTOLOGY 



make mistakes. These can be rectified if the specimens 

 are available, but must always remain as sources of 

 further error and confusion if the printed name has no 

 solid backing. 



(II) REGARD FOR STRATIGRAPHICAL POSITION 



The precise horizon from which a fossil was collected 

 is one of its most valuable qualities, whether it is destined 

 for geological or biological treatment. This point can 

 easily be determined at the time of collection (unless the 

 specimen lay on a spoil heap, when due note of the fact 

 should be taken, and attempts made on the spot to trace 

 its actual provenance), but it cannot be subsequently 

 deduced with certainty. Before undertaking an expedi- 

 tion, it is well to study available accounts of the district 

 and strata to be visited, so that determined stratigraphi- 

 cal divisions can be recognized. But in any case, the 

 first duty for a Palaeontologist, on his arrival at an 

 exposure, is to note, and if possible to measure, the 

 more striking features of lithology and bedding shown 

 in the rocks. Not until this is done should any collect- 

 ing begin. Since the fossil-evidence may often supply 

 other, and better, indications of zonal horizons than 

 mineral qualities, the first sketch of the exposed rocks 

 may need revision. It is usually best to fix on some 

 prominent and persistent feature (such as a shale-band 

 in limestone, a calcareous layer in shale, or a flint-bed 

 in chalk) as a datum from which vertical measurements 

 can be made ; the distance above or below such a line 

 at which any fossil or fossil-band occurs should, where 

 possible, be recorded. It is not enough to gather all the 

 fossils from one quarry into a separate group, nor even 

 to distinguish between those from upper and lower parts 

 of the section. Too much precision in this matter is 



