The impact of urbanization on construction minerals
Construction minerals (sand, gravel and crushed stone used in the production of concrete) are among our most plentiful mineral resources by volume. Increasing quantities of these materials are required for construction within urban areas. However, continuing and accelerating suburbanization is rapidly making unusable deposits of these minerals due to zoning and other restrictions. In addition, the low intrinsic value of mineral aggregates and their bulkiness make the economics of the industry extremely sensitive to location. Mathematical programming is used to investigate the economic impact of urbanization on the production and distribution of construction minerals.
A Planning Model for Construction Minerals
The problem of allocating construction minerals is rarely considered by those who plan the destiny of our urban environment. The purpose of this research is: 1 to delineate in dollar terms the magnitude of the result of not planning for the consumption of construction minerals, and 2 to develop a computer simulation model which will provide planners with an indication of the effects of decisions. affecting these resources. 
 
Construction mineral aggregates sand, gravel, and crushed stone are among the earth's most plentiful, yet are rapidly being rendered inaccessible in those areas which need them most. They are characterized by a low intrinsic value, a high bulk, and a delivered price which is very sensitive to the transportation cost associated with moving them from the quarries to their points of demand, It is ironic that the cities which create the demands for mineral aggregates are, at the same time, preventing their extraction by being built over them or by legally limiting their use through zoning restrictions. 
 
The simulation model which has been developed enables the planner to investigate the effects of various zoning strategies. It allows him to investigate the results of limiting individual operations and to force the removal of material from a site before it is covered by urban development. It does not attempt to search for decisions which yield “optimal” solutions; rather it indicates the results, over a simulated time period, of various planning strategies, thus providing the planner with greater insight into the effects of the decisions that he alone can make.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.