80 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
kinds, detailed areal mapping and general summaries. Under the 
first class of work large areas have been covered in the Appalachian 
coal field, and the results have been published in numerous folios. The 
work in Pennsylvania and West Virginia has been carried on by 
Campbell and his assistants; in Tennessee by Campbell, Keith, and 
Hayes, and in Georgia and Alabama by Hayes. Work has also been 
done in southern Indiana by Campbell, Fuller, and Ashley; in the 
southwestern field in Indian Territory by Taff and Adams; in the 
Rocky Mountain fields in Montana and Colorado by Weed, and in 
the Pacific fields by Diller, AVillis, and George Otis Smith. 
The principal work of the second class has been the preparation of 
a series of papers, 12 in number, summarizing existing knowledge 
relating to coal fields of the United States. These are more fully 
described on later pages. 
The investigation of oil and gas fields has only recently been taken 
up. During the last year certain portions of the Appalachian field 
have been studied by Campbell, Griswold, and Fuller. The work of 
Griswold in the Cadiz field is especially noteworthy, since it is the 
most successful attempt thus far made to work out the structure of 
the oil-bearing sands by instrumental means and with a high degree 
of accuracy. A thorough reconnaissance of the oil fields of Califor- 
nia has been made by Eldridge, and of the Texas-Louisiana fields by 
Hayes and Kennedy. The Boulder oil field of Colorado has been 
studied by Fenneman. 
All known asphalt deposits of the United States have been exam- 
ined and reported upon by Eldridge, and those of Arkansas and 
Indian Territory have been examined in detail by Hayes, Adams, and 
Taff. 
A general reconnaissance of the clay resources of the United States 
east of the Mississippi River has been made by Ries, and his report 
is now in press. Detailed studies of particular deposits have been 
made by Vaughan in Georgia and Florida, and by various geologists 
in connection with their areal mapping. 
Important economic work has also been done under the section of pre- 
Cambrian geology, especially upon the iron ores of the Lake Superior 
region. All of the iron-bearing districts have been studied by Van 
Hise and his assistants, Clements, Bay ley, and Leith, and reports are 
either published or in press. Also under the supervision of Van Hise 
the lead and zinc mines of the Mississippi Valley have been examined 
in the Ozark region by Bain, Adams, and Tangier Smith, and in 
western Kentucky by Ulrich and Tangier Smith. 
