What other rocks may take the place of these principal rocks? Where do the metamorphic rocks occur? What is their thickness and amount? SECTION V. How many systems of fossiliferous rocks are there, and what are they? What other system is provisionally introduced? What is its position? [Illustration: Fig. 7.] Describe it. What materials of value are obtained from this system? [Illustration: Fig. 8.] What fossils does it contain? In what localities is it found? What explanation, in reference to these rocks, is given by those who deny that they constitute a distinct system? [Illustration: Fig. 9.] [Illustration: Fig. 10.] In what respects does the State of New York present the best facilities for studying the Silurian system? Describe the Champlain division. [Illustration: Fig. 11.] The Ontario division. The Helderberg division. [Illustration: Fig. 12.] [Illustration: Fig. 13.] [Illustration: Fig. 14.] [Illustration: Fig. 15.] [Illustration: Fig. 16.] Describe the Erie division. What are the fossils of this system? [Illustration: Fig. 17.] Describe the Crinoidea. The Cephalopoda, and the two forms. [Illustration: Fig. 18.] The Trilobite. What higher forms of animal life existed during the silurian period? The geographical range of the system? Of what does the Old Red Sandstone consist? Describe its three divisions. What are its fossils? [Illustration: Fig. 19.] Describe the fishes of that period. What was the peculiarity of the Pterichthys? Of the Cephalaspis? Where are the rocks of this system found? How is the carboniferous system divided? Describe the carboniferous limestone. What ores are found in it? Describe, its fossils. Describe the millstone grit. Of what do the coal measures consist? How does the ironstone occur? Describe the coal beds. How is the continuity of the strata interrupted? What variations from this general type occur in the formation? [Illustration: Fig. 20.] [Illustration: Fig. 21.] Describe the several varieties of coal. How is the coal quarried? [Illustration: Fig. 22.] What mineral springs occur in this formation? To what uses is coal applied? (The coal was deposited thousands of years ago, and has served no useful purpose, that we know of, till very recently. Its formation was planned and completed to meet a want which was not to be felt till the lapse of many ages. It is a notable instance of the wisdom and forethought, as well as of the benevolence, of God.) In what does this prospective arrangement consist? What are the character and position of the fossils of the coal measures? [Illustration: Fig. 23.] [Illustration: Fig. 24.] [Illustration: Fig. 25.] [Illustration: Fig. 26.] What are the four most abundant forms? Describe the Stigmaria. The Sigillaria. The Lepidodendron. The Calamite. Where are the beds of coal found? What is the fourth formation of rocks? Into what two portions is it divided? Of what does the Permian portion consist?