Ward — Geology of 'the Little Colorado Valley. 405 



The Shinarump. 



This constitutes a vast series with a maximum observed 

 thickness of at least 1600 feet. It presents a number of 

 phases, some of which are so distinct that if studied in only 

 one locality they would naturally be regarded as separate sub- 

 divisions, but such a general survey as I have been making 

 points to a certain homogeneit}^ in all these beds, or at least 

 establishes the unmistakable tendency towards the recurrence 

 in any of the phases of features that are prominent in other 

 phases. The Shinarump constitutes the horizon of silicih'ed 

 trunks and there is no part of it in which fossil wood does not 

 occur in great abundance. It also marks the limit of the 

 wood-bearing deposits of this region. For this reason alone, 

 in view of the etymology of the name, I should be justified in 

 extending the Shinarump as far as the fossil trunks occur, and 

 it is obvious from the language used that Major Powell had 

 the upper portions of the formation in view as well as the 

 lower when giving the name, although other geologists in 

 speaking of the Shinarump usually seem to have in mind only 

 those beds which I include- under the conglomerate. It is 

 doubtful, however, whether the remainder of the formation 

 has really been studied or carefully observed by others, and 1 

 fancy that in dealing with it I am entering upon a sort of 

 geological terra incognita. 



The Shinarump Conglomerate. — I am using this expression, 

 which is the one most commonly found in works that treat 

 of these beds, in a somewhat comprehensive sense, the necessity 

 for which will be apparent. As thus used this part of the 

 Shinarump occupies the lower half of that series and has a 

 maximum thickness of 800 feet. Although perhaps the most 

 prominent feature of it is the so-called conglomerate, which 

 sometimes is in truth deserving of that name, and contains 

 somewhat large but always well-worn pebbles and cobbles 

 derived from underlying formations, still, it rarely happens 

 that this aspect of the beds constitutes the major portion of 

 them. In the first place the conglomerate tends to shade off 

 into coarse gravels and then into true sandstones. These 

 sandstones are of a light color, contrasting strongly with the 

 dark brown sandstones of the Moencopie beds already described. 

 They are, moreover, always more or less cross-bedded and 

 usually exhibit lines of pebbles running through them in 

 various directions. These are true sandstones, very hard, 

 devoid of alumina, and scarcely affected by the winds, so that 

 their angles are usually sharp and the ledges they form are 

 abrupt and jagged. Although the sandstones proper generally 

 occur lower down, still, there is no uniformity in this arrange- 

 ment, and sandstones are often found in the middle and con- 



