two steps downward in the scale of animal. existence, appear farther and farther back toward the beginning. That the lowest four subkingdoms, together with the mollusks, worms, and arthropods, should seem to have been introduced abruptly and at the same time, apparently furnishes a decided objection to the origin of the higher forms from previously existent lower ones, as the development theory assumes. But to this objection there is a very easy answer; namely, that we do not know what the earliest forms of life were.

The eozoic rocks of the earth, so far as they are now known, show evidence of having been intensely heated since they were deposited; and they have, as a result of crystallization or even melting, become so greatly changed in their structure, that it would indeed be strange if any fossil could have been preserved

in them.

Common chalk is a rock composed mainly of the shells of many kinds of foraminifera, - representatives of the rhizopods.

It has been ascertained that the present seabottom is in many cases slowly building up by the deposition of foraminiferal shells, forming a chalk-like material. Most of those limestones of the world which lie embedded between layers

of other kinds of rock are composed mainly of the shells of rhizopods. Now, such limestones (that is, of this interbedded character) are found in abundance in the eozoic rocks; and among the same rocks are found many layers of graphite [black-lead].2 This is a most important and suggestive fact; for graphite is in some instances known to have been produced from fossil remains of plants; while there is no proof that it has been formed, or could naturally be formed, out of any thing but animal or plant remains.

There are ample proofs of the existence of a wealth of life in the Archæan rocks, from the

FIG. 17. Foraminifera.

presence of the above-mentioned limestones and graphites.

1 Dana's Manual of Geology, p. 158.

2 Dr. Dawson estimates the total amount in one band of limestone in the Ottawa district as equivalent to twenty or thirty feet of graphite. At St. John he thinks he has found a fibrous structure in the graphite, an evidence of its having been formed from land-plants. — GEIKIE's Text-book of Geology, p. 639.

graphites. From the high temperature of the sea-water on the surface of the cooling earth, it is probable that the conditions of existence. in the eozoic were such as to restrict vegetable life to the simplest algæ and animal life to pro

tozoans.

But, since the eozoic lasted for an immensely long period before the beginning of the palæozoic, there may well have been time for the development, from protozoan ancestors, of any or all of the low forms of life found at the beginning of the silurian age. There is, then, in the known facts regarding the kinds of life found at the beginning of the palæozoic, no contradiction of the theory of descent.

A strong argument in favor of the theory is based upon the fact, that, as a rule,1 the lowest animals and plants of each type are the first introduced, and that the subsequent history of the type is one of progress, both in the number of species and individuals, and in the complexity of organization or the perfection of structure, of the animal or plant.

The period of highest development of each group is usually followed by a concluding period of dwindling away, in which the numbers diminish, and the species become dwarfish,

1 Subject to a few exceptions.

changes mainly due to the influence of less favorable conditions of life. Any class of animals may fairly be said to advance in the scale of being, when out of aquatic forms it first gives rise to terrestrial ones. Of such advances a most striking one took place in the beginning of the carboniferous age, extending through many groups of animals, and over wide regions, both in the eastern and the western continents.

The first mollusks were of a type so closely allied to that of worms, that many of the ablest zoologists now follow the example of Professor E. S. Morse in ranking them as members of the sub-kingdom Vermes. In this case we have an illustration of the important general law, that the earlier members of any group of animals are frequently of comprehensive types; that is to say, they resemble the members of two or more later groups, which may be very distinct from. each other.

The appearance of such animals as the Archæopteryx affords a perfect illustration of this

law.

This was a bird whose fossil remains were first found at Solenhofen, Bavaria, in 1861.

1 For a full account of the matter, see Professor Morse's paper, Proceedings Boston Society of Natural History, vol. xv. March 19, 1873.

"In 1879 Professor Carl Vogt made a communication respecting a fresh specimen of this ancient bird, found in the same deposits which afforded the previous specimen.

The new specimen was singularly complete; and its wings were unfolded, as if death and fossilization had overtaken it in the act of flight. Its examination revealed certain startling features, which only serve to confirm in an un