348 PALEONTOLOGY 



(Lithodomus, Pholas, Teredo). Sometimes when a shell is 

 bored into, the material filling the boring may resist 

 subsequent solution better than the shell itself, and a 

 cast of the boring may result. 



All these various ways of preservation must be borne 

 in mind by the intelligent collector when at work on 

 cliffs and quarries. While the spoil-heap of a quarry 

 will often provide the choicest specimens, he should 

 never neglect to search for fossils in situ in the undis- 

 turbed rock. Only by so doing can he know whether all 

 the fossils belong to one fauna, or whether there are 

 several, and through what thickness a single fauna per- 

 sists ; only so can he see whether lamellibranchs, for 

 instance, are in the vertical position of living burrowers 

 or in the horizontal position of drifted shells ; only so can 

 he distinguish with certainty the presence of derived 

 fossils, whose original home was in some older bed and 

 whose worn and rounded surface distinguishes them 

 from the contemporaneous fossils with which they may 

 be mixed. 



The collector would be well-advised not to attempt to 

 clean or select his fossils on the spot where he obtains 

 them, except when their weight is serious. Many a good 

 specimen has been spoiled by the attempt to clean it on 

 the spot. Even broken specimens may often prove to 

 show special features not seen in perfect examples. The 

 writer once picked up seventy-three specimens of 

 Chonetes laguessiana from the Carboniferous shales of 

 Fourstones (Northumberland). They all looked alike 

 at the time, but on cleaning and sorting them at leisure 

 afterwards, fifty-eight were found to be complete speci- 

 mens but with the dorsal valve crushed in ; fourteen were 

 ventral valves, and one was a dorsal valve showing both 

 external and internal features. That one dorsal valve 

 would probably have been lost had any attempt to clean 

 or select been made on the spot. 



