310. THE HEIDELBERG BASIN 



a beetle complete the list of fossils from the Heidelberg 

 outlier. It is certain, however, that a considerable 

 variety of fossils will be found there in the future. The 

 varied nature of the scanty remains mentioned above 

 show that many classes of organisms were represented 

 in the waters in which the Heidelberg beds were de- 

 posited, and only careful searching is required to pro- 

 duce good specimens. The most favourable localities 

 for fossil hunting in that district seem to be the Doom 

 Eiver Valley west of Heidelberg village, the Spiegel 

 Eiver Valley, and the Klein Vette Eiver north-west of 

 Eiversdale, but in course of time new exposures will 

 be opened up along roads, and for various other purposes, 

 in places where the rock underlying the soil cannot now 

 be seen. 



The beds in which the fossils have been found are 

 grey or whitish in colour ; the red clays, sands and 

 marly beds seen to the north of Heidelberg have not 

 proved fossiliferous. It is generally found that red- 

 coloured rocks are not fossiliferous. The red colour is 

 due to the higher state of oxidation of the iron com- 

 pounds than is the case in the green, blue and grey 

 rocks ; when much organic matter was present during 

 the deposition of the mud, the red, highly oxidised, iron 

 compounds were reduced to a less oxidised state, and 

 these give a bluish-green or grey colour to the mud. 

 The amount of organic matter present was of course 

 closely connected with the number of living organisms 

 that might leave traces of their existence in the shape 

 of fossils, hence it is always to be expected that beds 

 that are uniformly red throughout, and therefore to be 



