Meyer, Gary N.Jirsa, Mark A.2010-03-122010-03-1219840544-3105https://hdl.handle.net/11299/5931316 p., 2 plates. 1, Sand and gravel; 2, Bedrock. Scale 1:250, 000.Aggregate is derived from two major sources in the seven-county area. Surficial deposits of sand and gravel, or "natural" aggregate, are the primary source. These are deposits of rock detritus broken down and sorted by the actions of glacial ice and running water. A second and increasingly important source is carbonate (limestone and dolomite) bedrock, which is converted to aggregate by blasting and crushing. Because ongoing urban development both restricts access to sources of aggregate and requires more aggregate for construction, a report was published by the Metropolitan Council of the Twin Cities area as an aid for industrial and governmental planners dealing with the problems of aggregate supply and demand. The plates and Appendix A of that report summarized the data in this information circular.engeologyaggregateMinnesota Geological SurveyresourcesTwin CitiesMap