100 Dynamic Theory. 



afterward. In this respect the snakes show improvement since their 



separation. 



Again, Dana remarks that the Trilobite, which was among the first 

 Crustaceans, was superior to the Barnacle, which did not appear till the 

 middle of the Reptilian Age. But the origin of the Barnacle was very 

 probably by development from the Ostracoids, and a late off-shoot. 

 The Ostracoids have run from the Silurian to the present time, under 

 varying genera, and may have developed more than one articulate off- 

 shoot. 



Dana observes further that Mosses and Lichens appear after the 

 Acrogens of the Carboniferous era* 



This may be accounted for in more than one way. Both Mosses and 

 Acrogens are derived originally from the great Algae family. There 

 are many different forms of Algae, and one form may have been the 

 ancestor of a Moss and another of the Acrogen. Placed under different 

 influences their evolution might have advanced at very different rates, 

 and the conditions necessary for one development have been retarded 

 ages behind the other. A fungus like a mushroom is of the simplest 

 form and the most limited function, yet it is of comparatively recent ori- 

 gin, because, having no powers of its own for the manufacture of food 

 from the mineral kingdom, its life could begin only after better equipped 

 orpanisms had existed and prepared food for it. See chapter on 

 Fungi. 



Another remarkable circumstance is that sometimes the first animals 

 of a family or order that appear are too different from that family 

 which went before to warrant the belief that the last could have been 

 derived from the first by modification or development. 



Thus the Trilobite appears in the Lower Silurian, with no remains of 

 immediate relations to show his lineage and connections. He was 

 undoubtedly originally from the worms, and possibly his immediate 

 ancestors may have lived in the same seas, but like the other worms 

 have been destitute of an organization that could be preserved. But I think 

 it more probable that he was an immigrant where found in this country 

 and Europe. Between the end of the Laurentian and the beginning of 

 the Silurian time there was a vast lapse of time in which nothing in the 

 way of rock building was .done on these two continents. The rocks of 

 the early Laurentian times were being slowly raised and tipped up dur- 

 ing a period of some millions of years, then held out of water exposed 

 to the erosion of the elements till they were robbed of a mile or two of 

 their accumulations. They were then in part sunk again slowty into 

 the sea, and the work of building the Potsdam formations on them was 

 commenced as they went down. The time during which this movement 

 was going on is entirely unrecorded in any strata that are accessible to 



