PREFACE. 
FOR many years the third part of the Manual of the Geology of India 
(Economic Geology : by V. Ball) has been out of print and several 
projects have been formed for the production of a new edition. Under 
the first of these it was proposed to re-issue the publication in a series 
of separate volumes, each dealing with a single mineral, and a beginning 
was made with Corundum (by T. H. Holland) in 1898. It soon became 
clear, however, that this method of re-editing would extend over a very 
long period and the question of reproducing a revised manual on the 
original lines was reconsidered ; articles were prepared by various 
members of the Geological Survey, but, pending the completion of the 
whole volume, were not published ; it is hoped that the work will be 
issued before long in a short form with an extensive bibliography and 
in the meantime it has been decided to publish such articles as are likely 
to be of immediate interest. One of these is the article on coal, which 
was revised by Mr. R. R. Simpson, now Inspector of Mines, while he 
was still attached to the staii of the Geological Survey ; this he has now 
further revised and brought up to date. I am indebted to Mr. G. F. 
Adams, Chief Inspector of Mines, for permitting Mr. Simpson to under- 
take the work. 
H. H. Hayden, 
Director, Geological Survey of India. 
