72 Dynamic Theory. 



and by means of which his accretions and excretions take place. He 

 has no mouth, stomach or permanent members. Sometimes these ani- 

 mals live in families or communities, their shells being massed together 

 in various forms, but in all cases each shell or cell contains a single 

 simple one-celled animal. It is from the accumulations of the remains 

 of this kind of animals that we are to presume the limestone beds of 

 the Laurentian were formed, in all, two-thirds of a mile in depth. It is- 

 not probable that any orders of animals of much higher organization 

 than these existed in America before the Silurian times. 



The plants to which the origin of the graphite is attributed, were also 

 of very simple organization. They were all algse or sea weeds and of 

 the lowest order. But they must have existed in immense quantities 

 to form an amount of graphite equal to thirty feet in thickness. Dana 

 estimates that a bed of bituminous coal requires for its formation not 

 less than eight times its bulk of compact vegetable debris. And an- 

 thracite requires twelve times its bulk. Graphite would require much 

 more still. So that it is safe enough to estimate that the remains of 

 five hundred feet in depth of solid vegetable matter is represented in 

 the Laurentian formations, beside what was turned back into carbonic 

 acid in the fearful scorchings of the metamorphic ages which in all 

 reason must have been an enormous amount. It is assumed that all 

 this vegetation consisted of algae, for the reason that these plants are 

 the simplest on earth, and that they are the only sort of vegetation to 

 be found in the long Silurian ages following the Laurentian. They are 

 the most versatile and hardy of all plants, can live on the rankest and 

 rawest of mineral compositions and in the greatest variety and extremes 

 of temperature. As these algae, no doubt, furnish us with the earliest 

 examples of plant life that we are acquainted with, it may be well to 

 describe some of them. The simplest forms are the protophytes, the 

 diatomacese and desmidiacese, or, for short, diatoms and desmids. 

 These have but a single cell and are microscopical. Their mode of 

 propagation is by fission. In the mature plant a partition is formed, 

 the protoplasm contained in the case of the cell dividing into two parts, 

 each part growing into a complete cell, when they become detached. 

 The protococcus is of another order of algae, and while only single 

 celled like the diatom, differs in function. It has red coloring matter 

 in it, and reproduces by its internal colored protoplasm forming into 

 several separate spheres or spores. As these grow, in a few hours they 

 burst the shell and escape. Many of these spores are carried every- 

 where by the air. They grow on rocks and in the snow in Greenland 

 and Sweden, giving the snow a red color. They also grow in the Red 

 Sea and give it its color. It is likely that these infinitesimal plants, 

 through their very rapid reproduction, may have contributed toward 



