190 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1021. 



Corliiriil:!. and not las ono might expert) l)elon;-;int; to the 

 more eomnion group of Spharrium or risidiiini. There is 

 also the imprint of a small loaf resomliliug a willow, and 

 numerous lime tubes whirh seem lo ha\e heen formed 

 around roots or small vegetalde stems. 



Microscopic examination of the specimen 

 found near Osborne's Well shows that it is very 

 porous and is composed almost exclusively of 

 calcareous matter in fragments of diverse 

 shapes, with a few angular fragments of quartz 

 and feldspar. The lime tubes mentioned by 

 Mr. Dall are prominent in the thin section. 



In a specimen of thin-lu'dded limestone from 

 the east end of the Clan ton Hills Mr. Dall 

 foimd pseudom,orphs of cypridian crustaceans 

 like those he found in the other specimens men- 

 tioned. In one of the calcareous beds in 

 Osborne Wash Blanchard " also found fossils, 

 which Ml-. Ball identified as the gastropod 

 Bitthini and a prol)able young Corbicula. He 

 states: "There is nothing incompatible be- 

 tween the presence of Bittiuni with Goniohnsis 

 and Cnrbicula in the sanu' tleposit. All are 

 prone to inhabit brackish water, especially 

 near seashores." He also says: "There is no 

 clue to the age of the deposit except that it is 

 doubtless Tertiary. " 



QUATERNAKY FORMATIONS. 

 SEDIMEXT.VRY FORMAT[ONS. 



Definition. — The unconsolidatc^d and poorly 

 consolidated gravel, sand, and silt that fill 

 the valleys and fli or the flood plains of the 

 rivers in this dese?'t region are of (Quaternary 

 age. Basalts which are dcaiiy .-dso Quater- 

 nary are interliedded wilh or resi upon these 

 sediments. 



Distrilxdion and chanictir. —The valleys 

 throughout this area, like neaily all other desert 

 valleys in the Southwest, are dee|)ly filled with 

 dcdiilal matei-ial, for the most ])art unconsoli- 

 dated or poorly consolidated, derived fi'om the 

 mountains. The thickness of tliis material in 

 the valleys has not l)een <leteiiiune(l. It is cer- 

 tainly to lie measured in hundreds if not in 

 thousands of feet, as is indicated liy records of 

 wells in a, number of the valleys. 



The character of the material varies greatly, 

 as is to be expected in sediments laid down by 

 generally slioit and usually disconnected 

 streams mider arid conditions. In the flood 



11 Blanchard, R. C, op. cit., )>. 39. 



plains of Gila and Colorado rivers and in certain 

 clay ilats.or playas,in interior valleys there are 

 very line silts or clays, l)Ut the major portion 

 of the till in the valleys is sand and gravel, 

 in places very coarse. Much of it is poorly as- 

 sorted, consisting of coarse sediments in a clayey 

 matrix. The surface layers in most of the val- 

 leys contain silty soil more or less mixed with 

 gravel. This soil, where it has been properly 

 irrigated, has proved to be highly productive. 

 In Castle Dome Plain, Palomas Plain, and to a 

 less general extent in a number of the other 

 valleys in the area the wind has removed the 

 surface silt, leaving a residual floor of gravel. 

 Sand dimes are common in Cactus Plain and 

 also occur in Eagle Tail \ alley. 



In almost every place where the fill is in- 

 durated to any extent the cement is a calcareous 

 material called "caliche" and known also as 

 cement or hardpan. Lee '"* has described the 

 mode of occurrence of caliche and discussed the 

 theories as to its origin. He concludes that the 

 caliche in Salt River valley, which is essentially 

 similar to that in the lower Gila region, has been 

 formed in [lart by the deposition of carbonates 

 and other salts held in solution in the ground 

 water and in |iai-t by the evaporation of water 

 percolating downwartl from the surface. On 

 the old road across the Gila Bend Mountains, 

 west of Woolsey Tank, occur gravel beds with a 

 calcareous cement which has set so firmly as to 

 form a hard though friable rock. (See PL XLIV, 

 B.) These beds ai-e exceptionally indurated, 

 but caliche beds so hard that it is very difficult 

 to penetrate them with pick and shovel are 

 common in a number of jilaces in the region. 

 Such beds are known elsewhere in the Gila Bend 

 Mountains, in Nottbusch Valley, in Castle 

 Dome Plain, and in other localities. Wells 

 sunk in La Posa Plain and McMullen Valley 

 usually penetrate beds of caliche below uncon- 

 solidated gravel and sand. On the flanks of the 

 Plomosa Mountains, on the east side of La Posa 

 Plain, lie thick deposits of caliche-cemented 

 (Travel, some of which is auriferous.'" Similar 

 deposits occur on the flanks of the Dome Rock 

 Mountains west of this plain. 



Beds of green and yellow banded clay are ex- 

 posed in the terraces of Colorado River in the 

 Colorado River Indian Reservation near Parker. 



i« Lpc, W. T., UiidcrRroiiiirt waters o( Salt River valley, Ariz.: U. S. 

 Geol. Survey Waler-S\i])r)ly Paper 136, pp. 107-Ul, 19U5. 

 1^ Bancroft, Howland, op. cit., p. 88. 



