A First Year Course in General Science

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 edition. Excerpt: ...are assorted by the ocean currents and finally are made into sedimentary rock. (laboratory Manual, Exercise XIX.) Fig. 96.--Cathedral Spires In The Garden Of The Gods, Manitou, Colorado These rocks are of soft red sandstone. The highest is more than 200 ft. high. 1. In what position are the layers shown here? 2. What was their position originally? 3. What connection is there between their present position and the rate of erosion? 209. The Age of the Earth.--Just how long a time has been required to bring the earth to its present condition cannot be known exactly. One method of estimating the length of time is by calculation of the average rate of deposit in river deltas whose extent, a few hundred years ago, is known. The time required for the folding into mountains and the wearing down which have followed in some particular region must be ascertained by knowledge of the rock material and the agencies at work. The Appalachian Mountain system, about one hundred miles wide, was formed by the folding of strata of fragmental rock many thousands of feet thick. The accumulation of this material under the water is estimated to have taken at least thirty-six millions of years. Since that was done, it is thought that one third as much time has elapsed. Scientists conclude, from this estimate alone, that the earth must be many millions of years old. Another method of judging the age of the earth is by the study of fossils. A fossil is the remains or impression of a plant or animal that was buried in mud or sand. The mud or sand afterward became rock and thus preserved the hard parts of the body. The soft parts decomposed and passed off as gases or lig Fig. 97.-Fossil Fore Limb Of An Ancient Reptile A fossil hunter has been putting...