16 Missing Chapters of Geological History. 



species required to be introduced after certain important 

 changes that resulted in the destruction of all living things. 

 Without assuming: that this view is incorrect, it is at least 

 reasonable to inquire carefully what are the grounds of actual 

 fact on which it depends. 



The most ancient rocks hitherto determined within the 

 range of the British Islands are certain deposits of gneiss in 

 the north-west of Scotland. They are so completely meta- 

 morphosed, so far changed from their original condition of 

 stratified fossiliferous deposits, that no fossils, no trace of 

 organic contents, can at all be looked for in them. They 

 repose, however, altogether unconformably, on other beds of 

 gneiss, contorted and in the highest degree metamorphosed ; 

 and there can be no doubt that whatever the age of the over- 

 lying gneiss may be, that of the underlying rock is enormously 

 greater. The older gneiss must have existed as gneiss, the 

 strata must have been upheaved, denuded, depressed, and once 

 more elevated ; and they must have received the newer gneiss 

 as a submarine mud before any other of the British rocks were 

 formed. The newer gneiss is represented in Canada by rocks 

 that contain fossil corals ; at least, this is the opinion of the 

 able geologists who have examined the specimens. The hiatus, 

 then, that is indicated by the want of conformability between 

 these two ancient masses of gneiss may be regarded as the 

 earliest of the proved physical breaks in succession, and carries 

 us back to a period very long antecedent to the so-called 

 Silurian rocks with which geologists generally are familiar. 



On the gneiss of north-western Scotland lie strata now 

 called Cambrian. Similar rocks occur in Wales; but their 

 actual identity with those of Scotland is not proved. As described 

 by Sir Roderick Murchison, there appears to be a considerable 

 interval in Scotland, where the absence of the Lingula flags, 

 and the non-discovery hitherto of any fossils, renders it doubtful 

 how far the whole series is present. 



It is in the Lingula flags of Wales that we first come to de- 

 posits in any important sense fossiliferous. Here there are six 

 genera and twenty species of Trilobites — remarkable and easily 

 recognized animals, confined to Paleozoic rocks, but rano-ing- 

 through them, although becoming less important in the more 

 modern deposits. After the Lingula flags, the immediately 

 overlying deposits are strata long ago named by Professor 

 Sedgwick the Tremadoc slates. In Wales these are covered 

 by the Llandeilo and Bala Rocks, forming the Caradoc series. 

 There are in the Tremadoc slate no less than eleven genera of 

 Trilobites, seven of them distinct from those found iu the 

 underlying bed. All the species are different. A number of 

 Pteropoda are also found in the upper, but none in the lower 



