GEOLOGY OF THE ATLANTIC OCEAN. 47 



From whichever of these causes, or the combination of the whole, 

 we know that within the Laurentian time folded portions of the earth's 

 crust began to rise above the general surface in broad belts running 

 from northeast to southwest, and from northwest to southeast, where 

 the older mountains of Eastern America and Western Europe now 

 stand, and that the subsidence of the oceanic areas allowed by this 

 crumbling of the crust permitted other areas on both sides of what is 

 now the Atlantic to form limited table-lands. This was the beginning 

 of a process repeated again and again in subsequent times, and which 

 began in the Middle Laurentian, when for the first time we find beds 

 of quartzite, limestone, and iron-ore, and graphitic beds, indicating 

 that there were already land and water, and that the sea, and perhaps 

 the land, swarmed with animal and plant life, of forms unknown to 

 us, for the most part, now. 



Independently of the questions as to the animal nature of Eozoon, 

 I hold that we know, as certainly as we can know anything inferen- 

 tially, the existence of these primitive forms of life. If I were to con- 

 jecture what were the early forms of plant and animal life, I would 

 suppose that just as in the Palaeozoic the acrogens culminated in 

 gigantic and complex forest-trees, so in the Laurentian the alga*, the 

 lichens, and the mosses grew to dimensions and assumed complexity 

 of structure unexampled in later times, and that in the sea the humbler 

 forms of Protozoa and Hydrozoa were the dominant types, but in gigan- 

 tic and complex forms. The land of this period was probably limited, 

 for the most part, to high latitudes, and its aspect, though more rugged 

 and abrupt, and of greater elevation, must have been of that character 

 which we still see in the Laurentian hills. The distribution of this 

 ancient land is indicated by the long lines of old Laurentian rock ex- 

 tending from the Labrador coast and the north shore of the St. Law- 

 rence, and along the eastern slopes of the Appalachians in America, 

 and the like rocks of the Hebrides, the Western Highlands, and the 

 Scandinavian mountains. A small but interesting remnant is that in 

 the Malvern Hills, so well described by Holl. 



It will be well to note here and to fix on our minds that these an- 

 cient ridges of Eastern America and Western Europe have been greatly 

 denuded and wasted since Laurentian times, and that it is along their 

 eastern sides that the greatest sedimentary accumulations have been 

 deposited. From this time dates the introduction of that dominance of 

 existing causes which forms the basis of uniformitarianism in geology, 

 and which had to go on with various and great modifications of detail 

 through the successive stages of the geological history till the land and 

 water of the northern hemisphere attained to their present complex 

 structure. So soon as we have a circumpolar belt or patches of Eozoic 

 land and ridges running southward from it, we enter on new and more 

 complicated methods of growth of the continents and seas. Here we 

 are indebted to Le Conte for clearly pointing out that our original 



