866 PROCEEDINGS OF THE ACADEMY OF [DeC, 



with the exception of the above volcanic areas, for easily seventy miles 

 in every direction. Generally speaking the same rocks are exposed 

 in the Grand Canon of the Colorado, the canons of the Little Colorado 

 and of the stream known as Canon Diablo, which is distant to the south- 

 west and west only two and one-half miles. The cliffs exposed in this 

 caiion are composed entirely of the upper portion of the limestone bed 

 above referred to, as the caiion does not cut down to the underlying 

 light gray sandstone also referred to above, and the overlying thin red 

 sandstone stratum has been eroded off in this locality. In this crater 

 and around it are to be found nothing but stratified sedimentary rocks 

 or the fragments thereof. Viewed from the railroad across the per- 

 fectly level plain, Coon Mountain presents a very peculiar appearance to 

 anyone accustomed to study the sky line. Such an observer would 

 see a small mountain or butte, about one and a half miles long, rising 

 out of the level plain, the sky line of which (the rim of the crater) is 

 very irregular, the mountain differing widely in this respect as well as in 

 its light color from other mountains in the region, which show the 

 usual rounded appearance and gentle lines produced 1)y erosion, and 

 the dark color produced by the eruptive rocks of which they are com- 

 posed. 



Coon Mountain or Coon Butte, as it is often called, does not suggest 

 to one viewing it, especially at close range, from any direction, the 

 existence within itself of a large crater, approximately 3,800 feet in 

 diameter (its diameter along a north-and-south line passing through it 

 being 3,654 feet, while its east-and-west diameter is 3,808 feet) and 

 approximately 600 feet deep from the rim of the crater to the surface 

 of the interior central plain. It is a fact worthy of mention, but after 

 all just what one would expect when one realizes the cause of its origin, 

 that this mountain presents very much the same view to an observer 

 stationed several miles distant, whether he stands on the north, south, 

 east or west side of the mountain. This so-called mountain has an 

 extreme elevation of about 160 feet above the level of the plain, and an 

 average elevation of about 130 feet. Upon closer examination it is 

 found to be composed to a great extent on its outside slopes of an enor- 

 mous quantity of fragmentary material, which is made up as follows : 

 red sandstone fragments, limestone fragments, white sandstone frag- 

 ments and a few small yellow and brown sandstone fragments; the 

 largest masses probably weighing upwards of 5,000 tons (these are 

 nearly always limestone) down to silica in powder of microscopic fine- 

 ness (pulverized sand grains) which will be described hereafter. I 

 have made no attempt to compute the amount of this fragmentary 



