2o-G, by means of which the depth of the stratum, the thick ness of the stratum, as well as its projected dip may be determined by the application of these diagrams.
Fossils are essentially the remains of animals and plants, that existed during the various geologic ages, and are found to-day buried in the sediments. In this connection we may add, that in a strict sense, almost anything found in any state of preservation in the rocks, may be considered as fossils; thus footprints of animals, tracks of worms and mollusks, as well as burrows of various creatures, if properly preserved are con sidered as fossils.
From the beginning, animals and plants have been under going a great change, from a lower to a higher order, increasing and improving in their structure and form. It is known that animalsand plants as a species live for a limited time, then become extinct, and new species are formed, so it is established that certain groups did not extend beyond a certain geologic time; thus it becomes possible to use these remains of organism that we find embedded in the rocks and study the life that existed during the time of the formation of the stratum. As certain characteristic remains may be found in the various strata, they are used as "index fossils," as they indicate the life of a certain geologic period. By use of these fossils the geologist is enabled to correlate widely separated rocks, and prove that they are of the same age, and in many cases it is confirmed that they are por tions of th6 same stratum.
The hard or bony parts of animals and plants are preserved as fossils, therefore, the very earliest of living creatures that had no hard parts are not well known to us as fossils, and the first class of organism with which we become acquainted in the Cambrian (the Trilobites) are considerably advanced in structure and form.
In Paleontology two separate groups are distinguished, first the plant group (flora) and secondly the animal group (fauna), and each are in turn divided in smaller groups known as divisions or phyla. Each division and phylum is composed of animals or plants which are genetically connected.
The most ancient plants, those with simple structure, such as slime molds, bacteria, diatoms and other microscopic one celled plants, as well as alga or primitive sea-weeds are in this division. Sea-weeds quite often assist in building coral-reefs
by furnishing a large amount of the lime necessary. In this same class are also the fungi, of which toadstool, mushroom mold, mildew and yeast are familiar examples.
The plants of this division are advanced over the Thallophyta, especially in their mode of reproduction. The mosses arc the typical plants of this division. As the members of the two fore going divisions arc seldom found as fossils they are unimportant to the geologist.
Although the members of this division bear no true flowers and seeds (cryptogams), they are much more complex than the aforesaid plants. The best preserved fossils of this division are ferns. Equisatelas (horse-tail) plants with simple stems, have been known from the Devonian to the present, but like most plants they were abundant during the Devonian and Car boniferous. when vegetation was immense, and are well pre served in the coal measures. Lepidodendron is the best known fossil tree of the Paleozoic.
Highly organized seed-producing plants are in this division, and have two subdivisions, namely—(r) Gymnosperm or plants with seeds that are unprotected by any covering; ever greens and shrubs being typical of this subdivision. (2) Angiospermae are the plants of the highest order, and all the flowering plants, and most of the present known species of the plant life come under this subhead.
Protozoa are simple one-celled, generally microscopic animals, consisting mainly of protoplasm, usually without hard parts, and therefore, without any fossil remains. Under the class of Sarco dina we have relatively large marine and fresh water Protozoa, some visible to the naked 'eye, and in the subclass Rhizopoda (most important in geology) we have creeping forms and some, like Foraminifera have a calcium carbonate skeleton or test, with one or more chambers. They are mostly marine animals living in water free from sediments, and in the Mississippian period, Foraminifera became important rock builders, and the chalk of the upper Cretaceous, namely, the Niobrara, Austin and Rotten limestone formations are composed of Foraminifera combined with members of other phyla which are known to be shallow water forms, thus indicating that Foraminifera lived in shallow water.