Arizona republican., 1892-12-01
AGE OF THE EARTH.
A FASCINATING STUDY THAT IS FLU
 COATING A GREAT MYSTERY.


 These Computations Are Made.
 At the recent meeting of the British association a discourse was delivered by he president, Sir Archibald Gerkie, on one of the most interesting problems in modern science-the age of the world. Over century has elapsed since James Hutton wrote his "Theory of the Earth" which was the first attempt to formulate a chronology of creation in accordance with the discoveries of science; since then knowledge has made vast strides, and his followers have access to mass of information which he did not possess. Playfair and Kelvin improved upon his work, and now Gerkie and the school to which he belongs have gone beyond them.
 Geologists have ascertained that the rate at which erosion takes place can be measured; by applying their scale to the sedimentary rocks they have formed hypothesis as to the time which has elapsed since erosion began. To put the proposition in similar language, the sur face of the globe is constantly wearing sway under the influence of water and wind. Tine portions which are worn off are carried down to the sea or into hol- lows, where they are deposited and form sedimentary rocks. If we can ascertain how long it takes to form a sedimentary rock we can figure out when the progress of wearing away and redepositing began.
 Ar,h,hn1l efo thnf o able computation the stratifed rocks at- tain an average thickness of 100, 900 feet. The material of which they consist was all washed down from high planes, de- posted and left to stratify. By the in- spection of river banks it is found that in places the surface of the land which has been carried down as sediment in rivers has been reduced at the rate of foot in 730 years, while in other places, where the land was more stubborn or less flexible, it has taken 6,S00 years to lower the surface one foot. The deposit must be equal to the denudation. Thus we find that while some of the sedimen- tary rocks have grown foot in 73O years others have taken 6,S00 years to rise that height. Thus the period of time that vas required to build up l00,- 900 feet of sedimentary rock has varied according to locality from 73,000,000 years to 6S0,000,0O0 years. It follows that the active work of creation lasted for cycle intermediate between these two figures, The cycle varied with end less succession of periods of disturbance by volcanic force and glacial action, and the frequent submersion of dry land, alternating with the emerging of have retarded the growth of sedimen- tary rocks, but they cannot have accel- erated it.
 A study of fossils teaches the steady uniformity with which the work of creation proceeded. Since man began to observe there has been no change in the forms of animal and vegetable life. A few species have disappeared-not one new species has been evolved. Not only do we find the fauna and fora of ancient Egypt as depicted on monuments which are probably 5000 or 10000 years old identical with those which are found ill that country today, but shells which in- habited our seas before the ice age and grew in an ocean whose bed overlay the Rocky mountains are precisely the same species that are found in the Bay of Monterey and the waters of the Chesa- peake IL is evident that there has been no essential change in the conditions Of life since these animals and these vege- tables were first created, yet how vast the shortest period which we can assign to the gap that divides us from that re- mote epoch!
 Little by little the geologist is lifting the veil which covers the prehistoric record of our planet. The era which preceded the age of civilized man, with its vest rivers carrying down diluvial floods to the ocean, and the bursting forth of mountain ranges from contrac- tous Uf the earth's crust has been painted to the life. But no one has exercised his pencil on that preceding age, when the forests made way for clumps of stunted birch and willow, incessant snowfalls covered the plains, glaciers crept down from tine north, and gradually vast sheet of ice half mile thick drove man. kind with the mammoth and the rein deer to those fortunate regions which, like California, escaped the agony of the last ice age.
 Nor have we any distinct perception of that subsequent age when the ice melted or receded to the pole, or dense tropical jungle grew up in the morasses il had left, swamps steaming with trop- ical heat swarmed with uncouth ba- trachian and reptile life, trees of mon strous growth shed their shade over shiny pools and black ooze, and in the distance long mountain ranges whose fontaoel had not yet closed, poured a never ceasing flood of lava down their sides. This is page of history which is yet to be written, but the materials are accommodating, and the historian will not ho long wanting. San Francisco Call.
 Sweet Simplicity.
 A party of guests from well known