18 THE OEOLOGICAIi STRUCTURE, ETC. 



compilation, may be of use to other individuals engaged in 

 similar investigations, I have been induced to lay them before 

 the members of the Society. 



North America. — Australians are largely indebted to the 

 Americans for instruction in the art of well-boring, hence it is 

 not unnatural that attention should be first directed to a country 

 which counts its artesian wells by the thousand. The total 

 number of wells in the western part of the United States, as 

 ascertained by the Census of the year 1890, was 8,097. These 

 were found in North and South Dakota, Nebraska, Kansas, and 

 the states and territories to the west of these, and on to the 

 Pacific Coast. 



The United States Government, recognising the importance 

 of having an exhaustive scientific examination made of the arid 

 regions of the interior, with the object of amelioriating the 

 conditions of life therein, appointed a commission consisting of 

 geologists and engineers for this purpose, 



A perusal of the official reports of the Commission reveals 

 the fact that the great bulk of the supplies of water are drawn 

 from Cretaceous strata, to which may be added the less copious 

 yield of the Tertiary and Recent Beds. 



The Cretaceous Rocks of North America have been divided 

 into two series, an Upper and Lower, each of which has been 

 further subdivided by different observers into different horizons. 

 The relations of these formations have been very much mis- 

 understood, and the nomenclature much confused — different 

 writers having applied different names to the same formations. 

 Without entering into the much-debated question as to the 

 classification of the American Cretaceous Rocks and their 

 correlation, it will suffice for the purpose of the present paper to 

 mention that each series may be divided into an Upper, clayey or 

 impermeable, and a Lower, in which sandy or porous beds 

 predominate. 



The Potomac horizon lying at the base of the Cretaceous 

 may be traced from Central New Jersey through the Atlantic 

 and Gulf States to Northern Mississippi for a distance of fully 

 one thousand miles. The Dakota horizon is known only in 

 the interior part of the Continent, and is regarded by some 

 of the American geologists as forming the base of the Upper 

 Cretaceous. 



