424 HOLLICK. 



They invariably extend through the rock at, or nearly at, right 

 angles to the plane of stratification and are either straight or 

 sparingly branched. Where the ends appear on the surfaces 

 of the rock these give rise to little pits, usually encircled by the 

 rims of the limonite tubes. On breaking one of these nodules 

 open the structure and arrangement of the remains may be ob- 

 served. 



I have never seen any fossils in the Cretaceous clays which 

 are comparable to them, but roots of living plants which have 

 found their way down into ferruginous clays and sands often 

 produce very much the appearance of our specimens, and I am 

 inclined to think that these rhizomorphs represent the lignified 

 remains of former living roots, which were retained in their 

 original positions after the clay had been torn up and trans- 

 ported. During the subsequent hardening of the clay and the 

 oxidation of its contents, iron-bearing water followed along the 

 roots, gradually depositing a tube of limonite, while the vege- 

 table tissue was either destroyed or converted into lignite. 

 From this point of view our rhizomorphs would represent post- 

 Cretaceous preglacial vegetation. 



