The aim ofthis book isto provide a clear,up to date text coveringthe principles of oilwelldrilling engineering. It is the author's contention that it is necessary to start from first principles in order to give both student and practising engineer a compre!tensiveunderstanding of the subject. Hence, no prior knowledge of any topic is assumed, and all the necessary equations and calculations required in well design are presented. Full derivation of most equations isincluded, to enable both the engineer and the scientist to appreciate the limitations of the equations, and to allow the researcher to incorporate further refinements.

One of the results of the Danmark Expedition has been a very considerable and important extension of onr knowledge with regard to the marine, Jurassic and Cretaceous deposits of East Greenland and thus of the Arctic zone as a whole. The Expedition brought home a very complete material of these deposits, from regions whose geological structure had hitherto been quite unknown or only very imperfectly studied. This material was intrusted to me for investigation by the Committee for the Danmark Expedition, and as it proved to have come from deposits which were almost all younger than the Jurassic deposits investigated by the Danish expeditions of 1891-92 and 1900, in regions of East Greenland somewhat further south, and as no material for comparison existed in Copenhagen, the Committee voted me the necessary hinds for a journey to Munich. Here Professor Rothpletz with the greatest willingness permitted me to use the rich collections of the Pakeontological Museum there for comparison, and 1 would express my best thanks to him here for this permission. - On the return journey from Munich I made a short stay at Gottingen, where the well-known expert on the Jurassic deposits of the Arctic regions, Professor Pomi*kckj, was so kind as to look through a part of my material, especially the Ammonites. For the suggestions and information Prof. Pompkckj gave me on this occasion I am extremely indebted to him. As, further, a number of species occurred in the material, which had earlier been described by Tullbkho and Lunbobkn from the Jurassic deposits of Nova Zemhln and Spitzbergen, I desired to compare my material with theirs and journeyed to Stockholm on my return from Germany. For the friendly permission given me there to make the comparison, it is a pleasant duty to tender my best thanks to Professor G. Holm, the Director of the Zoopabontological Department of the Riksinuseum.

One of the first things discussed in an Introduction to Mining course and one which students must commit to memory is the definition of ‘ore’. One of the more common definitions (USBM, 1967) is given below:
Ore: A metalliferous mineral, or an aggregate of metalliferous minerals, more or less mixed with gangue which from the standpoint of the miner can be mined at a profit or, from the standpoint of a metallurgist can be treated at a profit.

Common challenges associated with grade uncertainty involve failing to meet decisive operational targets, which include (among others) the following: ore tonnage sent to the mill, total metal processed at the mill, blending requirements on ore feed, total waste tonnage mined, maximum allowable proportion of potentially deleterious materials (e.g., toxic elements such as arsenic). These challenges reflect, to an important extent, the uncertainty involved in defining precisely the mineral grades in an ore deposit. <...>