AMERICAN ASSOCIA TION FOR THE AD VANCEMENT OF SCIENCE. 307 



The speaker then conducted his hearers to the region lying north of the 

 chasm. The region through which it extends consists of carboniferous strata, 

 but about forty miles north of the river appear strata of later age, forming a series 

 ofterrar.es, each terrace being terminated by a line of gigantic cliffs, one thousand 

 to two thousand feet high, and of very wonderful sculpture and brilliant color- 

 the strata in this stairway of terraces are the remnants of beds which are stretched 

 unbroken over the entire district now drained by the Grand Canon, The total 

 thickness of the beds removed was more than ten thousand feet, and the divided 

 area more than thirteen thousand square miles. This denudation began in the 

 Eocene time, and has been continuous until the present. A great amount of up- 

 lifting has also occurred during the same period, varying according to locality 

 from sixteen thousand to nineteen thousand feet, and the present altitude of the 

 region is the difference between the amount of uplift and the thickness of strata 

 removed — /. e., seven thousand to nine thousand feet. The cutting of the 

 Grand Canon is thus merely the closing episode of a long period of erosion. 

 Captain Button states that the cutting of the present chasm is a comparatively 

 recent geological event, and probably had its beginning in the Pliocene time. 



The process of excavating the canon was then briefly explained. It consists 

 in the action of two classes of natural causes. The first is the scouring action of 

 the stream upon the rocks in its bed. The stream is a fierce torrent, carrying 

 large quantities of sharp sand, which acts like a sand-blast. A river will always 

 cut down its bed when the quantity of sediment it carries is less than it is capa- 

 ble of carrying. When this quantity is greater a part of it is thrown down upon 

 its bottom, protecting it from scouring. In this respect the Colorado is an excep- 

 tional river. The other process is weathering. The stream cuts a chasm no 

 wider than its water-surface. But the cut thus made is widened by the secular 

 decay of the walls of the chasm which, though slow to the perception becomes 

 great after the lapse of many thousands of years. The peculiar architectural pro- 

 files were explained as being due to different decrees of resistance afforded by 

 different beds to the action of weathering. Captain Button then exhibited views 

 of the grandest portions of the chasm. Although the magnitudes of the compo- 

 nent parts are very great, the highest sublimity is found in the sumptuous and 

 noble rock temples and beautiful sculpture of the walls, which show almost in. 

 credible resemblances to human architecture. The colors also are very brilliant 

 and rich. 



The Grand Canon is about two hundred and twenty miles long, from five to 

 twelve miles wide, and from five thousand to six thousand feet deep. Those who 

 have seen it all unite in declaring it to be the most sublime and impressive of all 

 natural features in the world. 



The first paper on the programme, in section A for the second day, was that 

 of J. E. Hilgard, " On recent deep-sea soundings in the Gulf of Mexico and Car- 

 ibbean Sea, by the United States Coast Survey," which, in the absence of its 

 author, was read by Br. W. H. Ball. The paper was well prepared and instruct- 



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