ECONOMIC FEATURES. 139 



formation may imbibe nearly all of the rain which falls upon it; another may 

 imbibe less than one per cent of it. 



Another stratum may become saturated and slowly yield its moisture to 

 agriculture, as in the case of the Ponderosa clay marls underlying the main 

 black waxy area; while another, like the upper Cross Timber sands, may give 

 up its moisture so rapidly, owing to its porosity, that it is poorly adapted, to 

 stand drouth and heat. Again, as has been said, one rock sheet may drink 

 in much of the rainfall and convey it through the pores to a lower region, 

 where by boring from above they may be tapped and come forth as abun- 

 dant artesian waters for a streamless and springless region. By the study of 

 the dip and extent of such a sheet, we have been enabled to accurately pre- 

 dict the extent and importance of an artesian area, the value of which, when 

 fully appreciated, to the people in the region in which it lies will be greater 

 in dollars than the cost of this survey; for by the simple knowledge of this 

 fact artesian water can be supplied to an area of 30,000 square miles of one 

 of the most fertile districts in America. 



Land Classification. — An important part of the work is the classi 

 fication of the lands of the region according to their agricultural, grazing, 

 mineral, quarrying, watered, arid, timbered, prairie, or other conditions 

 The work of the past year has already accomplished much in this direction 

 inasmuch as the general characteristics of areas have been determined, a nee 

 essary step for the more specific classification which must ultimately follow 



Steuctukal Material. — There is a great variety and abundance of build 

 ing materials of the Cretaceous formations, but the task of studying them is 

 so large that the work can hardly be considered begun. Building stones of 

 many qualities, paving stone, road material, cement stone, Portland cement 

 material, hydraulic cement material, fire-brick and tile clays, gypsum for 

 plaster of paris, sands for diverse uses, flint for glass making and sandpaper, 

 all appear in more or less abundant quantities in the Cretaceous rocks, and 

 need careful investigation and description. 



In their development lies a twofold source of wealth, in that they will not 

 only attract an intelligent capital to their development, but place in the hands 

 of our own people cheaper and more convenient building material. Among 

 the building stones there are are many varieties which deserve especial atten- 

 tion as worthy of export; while with chalks, clays, and every variety of mag- 

 nesian limestones, the region will no doubt become the centre of a great 

 American cement industry, like that of England, and such as can not exist 

 elsewhere in the United States, owing to the fact that it is in this region only 

 that the chalky formations upon which the English cement conditions are 

 dependent occur. One rock sheet (the Caprina limestone) already affords 



