REVIEWS 97 



half thick. Excavation has not yet been prosecuted beneath this floor. 

 The volcanic material is composed of fine fragments of glass. 



Bones, in an excellent state of preservation, recur in all the deposits 

 except the ash. They represent an Equus fauna of plains and forest 

 type combined, much richer in species than any Quaternary fauna 

 known from this coast. Among the larger forms represented are 

 Elephas, Mastodon, Megaloiiyx?, Rhinoceros, Equtis, and Arctotherium. 

 Many smaller carnivora are present, many of them of extinct species. 

 Among the rodents there is a new rabbit, a new squirrel, a new 

 Teanoma, etc. Two species of deer are represented by numerous 

 specimens. 



At the time of the accumulation of the case deposit, the topography 

 of the adjacent region had not assumed its present rugged character. 

 The case was formed by percolating waters during the cutting of the 

 McCloud river canyon. Infilling does not seem to have been contempo- 

 raneous with the excavation of the case. It is possible that much of 

 the accumulation in the case antedates the Red Bluff epoch. 



Further study will be required before the exact position of this 

 fauna in the Quaternary case can be stated. 



The Physiography of Southern Arizona and Neiv Mexico. By H. W. 

 Fairbanks. 



The great plain-like valleys of southern Arizona and New Mexico 

 are extremely interesting. They stretch eastward from Yuma, where 

 they are but slightly elevated above the sea, toward the continental 

 divide, where they attain an elevation of 5,000 feet. From this point 

 they gradually descend to 4,000 feet at El Paso, and are known to reach 

 still farther eastward toward the Gulf of Mexico. 



The plains are dotted with mountain ranges, which in southwestern 

 Arizona are completely isolated and rise very abruptly, but toward the 

 east the mountains break up the plain to such an extent as to form 

 nearly inclosed basins. 



A discussion of the origin of the nearly level surfaces of the broad 

 valleys of the southern portion of the Great Basin and those adjacent 

 to the lower Colorado led to the conclusion that three distinct types 

 are to be distinguished: (i) those produced by erosion, as in the 

 Mohave desert north of Kramer; (2) those of stream accumulation in 

 old valleys, formed by the coalescing of debris fans; (3) those of 

 accumulation in bodies of water. 



