44 LINKS WITH THE PAST [cii. 



Cambrian strata in which recognisable fossils first 

 occur. The rocks of the Cambrian and Ordovician 

 epochs, as represented by the grits, shales, slates 

 and other sedimentary strata in Wales, Shropshire, the 

 Lake district and elsewhere, though in places rich in 

 the remains of animals, aftbrd no information in regard 

 to the land vegetation. From the succeeding Silurian 

 epoch very little evidence has been gleaned as to the 

 nature of the flora, and it is not until we come to the 

 sedimentary rocks of the Devonian era that records 

 of plant-life occur in any abundance. The almost 

 complete lack of botanical data in the pre-Devonian 

 formations is in part due to the fact that these older 

 rocks consist to a large extent of marine deposits 

 formed under conditions unfavourable to the preser- 

 vation of plants. That the land-surfaces of the older 

 Palaeozoic eras supported an abundant vegetation 

 there can be little doubt. The relics of plant-life 

 furnished by the Devonian and succeeding formations 

 represent the upper branching-systems of a deeply 

 rooted and spreading tree, the lowest portions of 

 which have been destroyed or have left no sign of 

 their existence. 



In descending the Geological series, we begin with 

 superficial deposits, such as peat and river-gravels 

 found subsequently to the underlying boulder-clay of 

 the Glacial period. The remains of forest trees pre- 

 served in the peat and in submerged forests round 



