Geology of Lehigh and Northampton Counties, Pennsylvania: Historical Works

About >> Currency of the Geological Data

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Dave Anastasio and Frank Pazzaglia of Lehigh University's Earth and Environmental Sciences Department provided the following perspectives on the contemporary relevance of the Miller volumes.

The textual descriptions and the mapping within the Miller volumes are largely correct, but the names of some of the geological units have evolved over the years. For current usage, see the chart (PDF) "Stratigraphic Column for Bucks-Montgomery/Lehigh Valley/Pocono Region", which was created by Dave Anastasio, Carl Moses, and Frank Pazzaglia of Lehigh University's Earth and Environmental Sciences Department. It summarizes the major rock units exposed from South Mountain, through the Lehigh Valley, and up to about Jim Thorpe.

The chart's left-most column header is labeled "Ma", a geologic abbreviation for millions of years (literally, mega-annum). The numbers on the left therefore correspond to the beginning and end dates, in millions of years ago, of the geological periods and era indicated on the chart. The chart provides descriptions of formations (defined as "distinct mappable units"), as well as the depositional environments and tectonic events associated with them. It also identifies resources for which materials derived from the formations are used.

Another resource that may be consulted is the Stratigraphic Correlation Chart of Pennsylvania, published by the Commonwealth of Pennsylvania's geological survey (as of this writing, the third printing, slightly revised, 1993, is the latest version).

The usefulness of the geologic data in the Miller volumes continues to evolve. Current-day interest in the volumes will focus primarily on their implications for studying ground and surface water and also environmental issues such as sink holes and brownfield development. In an earlier day, the volumes were used to help determine where to construct quarries or coal mines. In the future the volumes will aid land use planners and municipalities by providing geologic information relevant to economic development.

The original maps for Lehigh and Northampton Counties are quite good, considering when they were done, and they served as a very valuable foundation for later geologic studies. One of the key differences between the Miller maps and later versions of geologic maps for these counties is the origin and nature of the rocks that underlie South Mountain. The Miller maps depict these rocks as being "in place" and extending deep down into the crust. In contrast, a more modern interpretation of these rocks is that they were transported here on faults from the east during collision with the African plate 250 million years ago. In general, while the geological 'perspective from above' of the maps is accurate, there has been some controversy about the vertical cross-section ('slice') perspective on the maps is accurate.

These comments about the maps pertain to the interpretation of the map data (as expressed in cross sections and text), not the data itself. Some publications predating the Miller work and most modern treatments of this region differ with respect to Miller's interpretation, not data.

Large-scale maps geologic maps of 7.5 minute quadrangles are available at the Pennsylvania Geologic Survey website. Links to them are provided in the Maps section of this website, as well as to map material at Pennsylvania State University. Links to the Pennsylvania Geologic Survey and USGS are provided for persons wanting further information about map coverage of Lehigh and Northampton Counties.