XXXV111 REPORT OF THE STATE GEOLOGIST. 



conditions to those described under the concretionary sandstones, and 

 the limonite or iron ore proper is found, as has already been men- 

 tioned, forming the capping of the higher hills of many of the eastern 

 counties. 



The mottled appearance of certain clays spoken of under the Coast 

 Clays is also observable in the clays of this division. 



The soils of the Timber Belt Beds differ with the underlying beds. 

 In the lowlands the soils are red clay, red sand, or mulatto, just as they 

 are underlaid by sands or clays respectively. The red color is due to 

 the amount of ferruginous matter they contain from the decomposition 

 of the glauconitic grains and pyrites, while the mulatto soil has its source 

 in the decomposition of the beds of greensand marls. These marls, in 

 addition to the glauconite they contain, which is itself a fertilizer of 

 great value, are frequently filled with fossil shells, the composition of 

 which increases their fertility to a considerable degree. For this reason 

 these soils are frequently quite as productive as those of the river bot- 

 toms, whose supply of lime is acquired from the sediment deposited by 

 the overflows of the rivers, which come to them through the great 

 district of Cretaceous rocks lying north and west, and have in suspen- 

 sion considerable quantities of carbonate of lime taken up in the jour- 

 ney toward the sea. Upon the upland we find a gray sandy soil, 

 grading downward into a red subsoil which is especially adapted to the 

 growth of fruit. 



Upon the Rio Grande these beds seem to rest directly upon the 

 upper beds of the Cretaceous, without the interposition of those lower 

 beds of the Tertiary which are present on the northern border, and 

 which will be described under the head of "Basal Clays." The Tim- 

 ber Belt Beds here show the same character of formation as is exhib- 

 ited in the east, and frequent beds of a large oyster, sometimes as much 

 as twenty feet in thickness, are found interstratified from the top to the 

 bottom of them. In general composition the various strata correspond 

 very closely to those already described, but owing to the indurating 

 effects of the dryer and hotter climate, there are certain remarkable 

 differences in present appearance. Thus the table land appears in the 

 west, as such, cut here and there by deep arroyas or incipient canyons, 

 while in the east only the remnants of it remain as the iron capped 

 hills. This gives to the western area a rugged appearance, which is 

 heightened by the almost total absence of timber, so plentiful on the 

 eastern border. 



