i894. MIGRATIONS OF EARLIEST FORMS. 419 



were thrown down, it is only to be expected that the Cambrian rocks 

 should vary considerably in importance in different areas, and there- 

 fore that the faunas also in some areas should be but poorly repre- 

 sented. Those parts which would be first encroached upon, if the 

 depression was very gradual, as we have every reason to think it 

 was, would contain the best record of the succession of life ; and all 

 recent researches have tended to show that the Cambrian faunas in 

 the areas bordering the North Atlantic basin are the richest in the 

 number of genera and species, and therefore contain the most perfect 

 record of the succession of life in the early rocks hitherto obtained. 



In a paper communicated to the Geological Society in 1875,3 

 which referred mainly to the European areas, I stated that " the 

 first fauna of which we have any knowledge occurs in the beds 

 furthest to the west, and there in earlier beds than any which occur 

 in the regions more to the east ; and though the forms which make up 

 this fauna belong to inferior classes, yet they are not the lowest types 

 in those classes, but often show evidences of considerable progression 

 in development. On this account I have often expressed the opinion 

 that we were far from the beginning of this type of life even in the 

 earliest Cambrian faunas, and that the forms had already undergone 

 many changes previous to this period. It is easy now to see how these 

 changes could have taken place, and moreover how it was that new 

 forms so frequently appeared at certain stages highly developed and with 

 no previous evidence in the rocks as to the changes they had under- 

 gone. The home of the earliest forms of life seems to have been 

 somewhere towards the south-west, and possibly not far from the 

 equator ; and it is from here that the various forms seem to have 

 migrated to the areas in which they were subsequently entombed. 

 The migrations seem to have taken place towards the North- 

 American continent very much about the same time as towards 

 the European ; and the sea-encroachments along that continent seem 

 to have been in a direction from south-east to north-west, so that the 

 lines indicating the two depressions would meet in mid-Atlantic. 

 This accounts for the great similarity in the two faunas, and for the 

 general resemblance offered by the order of succession of these early 

 rocks in the two continents. The higher lands in America would be 

 to the west and north-west, and the higher lands in Europe to 

 the east and north-east ; so that the last lands submerged would 

 approach each other and occupy the same region of the globe." 



When the above remarks were written, forms belonging to eight 

 classes had been discovered by us in the Lower Cambrian (now 

 called Lower and Middle Cambrian) in Wales ; and in a paper 

 in the Quavteyly Journal of the Geological Society (vol. xxviii., p. 173, 

 1872) I stated that : " These same groups are also more or less 

 present and tend to characterise these early deposits wherever 



3 Quart. Journ. Geol. Soc, vol. xxxi., p. 552. 



