Geologic sourcing of chipped stone artifacts and lithic debitage is a routine part of archaeological analysis and report writing (Figure 1). In order to do this task, a comparative collection is obviously necessary, one with solid geologic associations and an expansive geographic selection. Iowa’s bedrock contains a large variety of quality, knappable, lithic raw materials from both primary and secondary sources (Figure 2). Identification of archaeological specimens with a specific raw material is primarily accomplished by macroscopic analysis techniques geared toward achieving a “best fit” results (Figure 3).
The University of Iowa’s Office of the State Archaeologist (OSA) has an expansive lithic raw material assemblage with a nearly 30 year compilation history. The largest portion contains multiple samples of the lithic resources from within the state while the second portion contains multiple samples from the surrounding states and numerous additional states. During the late 1990s, a revision and reorganization of the OSA collection was begun in order to provide a more systematic and consistent approach to lithic source identification. This six year effort resulted in the first version of this web site posted in April 2006. The site was updated in 2008, again in 2011, and will be periodically updated as the physical assemblage expands and our knowledge of lithic raw material resources grows.
The In-State assemblage was revised on a structural level based on current understandings of Iowa’s bedrock geology (Figure 4). The physical samples were reorganized within drawers that represent the stratigraphic column of Iowa (Figure 5). The In-State assemblage holds 570 samples representing 75 different lithic types from 49 of Iowa’s 99 counties. The assemblage contains lithic types from the Quaternary, Pennsylvanian, Mississippian, Devonian, Silurian, and Ordovician Systems and from both primary and secondary contexts. Lithic types are arranged within geologic systems, alphabetically by county and then alphabetically by type name. The vast majority of samples have both unaltered and heat treated samples. As this web site represents raw material resources, all samples in this assemblage are collected from geologic sources only; no samples from archaeological sites are displayed on these pages.
The Out-State assemblage contains 318 samples representing 144 different lithic types from 21 states and one Canadian Provence. This portion of the assemblage is organized alphabetically by state with the samples from each state organized alphabetically by county. Priority efforts continue to expand the lithic raw materials from the six immediately surrounding states, which compose 60 percent of the total Out-State assemblage. Although many lithic types have both unaltered and heat treated samples, no systematic effort has yet been made to provide both.
Lithic Drawer Maps
This section displays the physical contents of the sample drawers housed in the laboratory at OSA (Figure 6). These drawer maps represent the physical drawers holding our lithic samples. There are headings for both the In-State and Out-State assemblages. Each drawer map contains 4 rows of 6 samples each for a total of 24 samples in each drawer (Figure 7). The sample order begins in the lower left corner and proceeds up and back in a sinuous patters ending in the lower right corner, which then flows to each successive drawer. Drawers for the In-State assemblage are labeled by geologic system following the stratigraphic column of Iowa. Each box for the In-State assemblage contains the sample name, county of origin, and catalog number. Drawers for the Out-State assemblage are labeled by state with each box containing the state name, county of origin, sample name, and catalog number. Drag the cursor over the sample name and an image of that sample will appear. Click on the sample name and larger images of all the samples in that drawer will appear. The normal type labels represents samples present in the assemblage while the shadow type labels represent those presently missing.
Lithic Data Tables
This section contains the current data on the lithic samples that compose the collection. These catalogs were created using Microsoft Excel. These data sheets can be downloaded for use either in Excel or HTML formats.
These three files, Geologic System, counties A-Z, and Lithic Types, present three different ways to search for lithic raw material information. The first is a listing of lithic types by geologic system association ordered after the stratigraphic column of Iowa. The second is an alphabetical listing of lithic types by county. The third is an alphabetical listing of lithic types by their type name. As noted previously, each of these data tables are available by clicking the link at the bottom of each page. You will get the complete data table for all lithic samples by choosing to view or download on any of the data pages.
The exposure type noted in the data tables and in the map keys are abbreviated. The following key identified the exposure type abbreviations.
Digitized Lithic Source Locations
All known lithic sources located on individual county maps have been digitized so this information can be coupled with the Excel lithic inventory for a GIS format. With the creation of a GIS for the Lithic Raw Material Assemblage, data can be use with a variety of base maps including Iowa Department of Transportation maps, 1:100,000 scale and 1:24,000 scale U.S.G.S. topographic maps (Figure 8). Orange areas indicate sample sites while the purple areas represent near or at surface bedrock as defined by the Geological Survey and Water Survey of the Iowa Department of Natural Resources. This has yielded a better picture of where our known lithic sources are. The Landform Regions of Iowa map will also be integrated into the GIS format for additional analytic potential. The current assemblage is the result of opportunistic sampling, leaving areas of the state possibly under represented or not represented at all. Additional samples are constantly being acquired and incorporated into the assemblage.
VBS Lithics Program (Under Construction)
Microscopic Lithic Samples
Microscopic viewing, using a dissecting microscope, has been applied in order to take a close-in look at surficial characteristics. Magnification levels of x7-30 powers provide clear views for sample comparison however, these scopes cannot capture images for further analysis, report preparation, or future comparisons. We recently acquired a handheld digital microscope that connects to a computer via USB cable. The scope provides two magnification powers of x20 and x400 and allows the user the ability to capture images and save them as JPEG files. This type of scope is readily available and affordable from various manufacturers.
We have taken x20 power images of all the Pennsylvanian System lithics representing roughly 72 samples of 13 types of lithics. They are presented in this section following the same format as the macroscopic samples described in the In-State section above.
The OSA’s Lithic Raw Material Assemblage is focused on expanding the assemblage and following four areas of research. The first is to address several geological association issues involving the designation of lithic materials and the specific formations or members they originate from. The second is to capture x20 power microscopic images of our entire lithic assemblage for a complete microscopic comparative section as noted above. The third area is the production of geologic thin sections of lithic samples. Six Pennsylvanian System samples are currently being processed for use in our assemblage as a result of collaborative research. Thin sections will provide the opportunity to study crystalline and optical characteristics of lithics and is a standard geologic analysis tool. And fourth, we are investigating the use of the University of Iowa’s Scanning Electron Microscope (UI-SEM). The University of Iowa’s Central Microscopy Research Facility (CMRF) provides Scanning Electron Microscope instrumentation and technical assistance. Using a Hitachi S 3400N we will be engaging in research to assess the viability of SEM application to the Lithic Raw Material Assemblage during the coming year. Results will be posted to this web page for all four of these areas of research as the data becomes available.
Macroscopic lithic analysis is a given in archaeological research and a collection of physical samples, geologically organized and geographically well documented, is a must. It is our belief that this assemblage will provide that resource. Since prehistoric artifact assemblages are so often dominated by lithic materials, a well-developed comparative assemblage could afford researchers the opportunity to address a myriad of issues including but not limited to trade, carrying capacity, the movement of people, and social interactions. The physical, geological, and geographical revision/reorganization of this assemblage are housed at the OSA lab, The University of Iowa. The web-based manifestation makes the OSA Lithic Raw Material Assemblage accessible from any place, throughout the Midwest, or even worldwide.
If you have any additional questions or comments about this page, or would like to discuss lithics with the authors, please feel free to contact either firstname.lastname@example.org; or email@example.com. We would appreciate hearing from you.
The Iowa Geological Survey at the University of Iowa, a division of the Iowa Department of Natural Resources, provides the following resources. They have been integral in assisting our research efforts. The following selections have individual web page addresses at the end of each section. The Iowa Geological Survey’s home page is:
PHYSIOGRAPHY OF IOWA
Today, Iowa is a prairie state having a generally moderate relief and gentle slopes. In some places there are broad uplands, in other places the valley floodplain is conspicuous. In general, the state is well drained by tributaries of the Mississippi and Missouri Rivers at its borders. Some parts of the state show extensive erosion, whereas other parts show little erosion and have distinctive constructional features. It is difficult to say which is the more important in development of the topography – erosion or deposition. However, the origin of the present surface is related very closely to the glacial history of Iowa. Several kinds of topography can be differentiated. The Mankato and Cary drift in northcentral Iowa are depositional terrain. So are the alluvial bottoms of the Mississippi and Missouri Rivers and the loess deposit bordering the Missouri River flatland. The Mankato and Cary surfaces have some of the characteristics of extreme youth of the erosion cycle of glaciated area with valleys just being formed and relatively poor drainage. The surface of the Kansan drift area is much more rolling and approaches the stage of maturity. The Iowan and Tazewell surfaces are intermediate in development but probably more erosional than depositional. In the “driftless area” of northeast Iowa the surface is even more mature.
Iowa’s Stratigraphic Column Text
Stratigraphic Column of Iowa, 2004
Bedrock Geology map of Iowa, 1998
Landform Regions of Iowa
Iowa is composed of a variety of landscapes or landforms. These are the surficial expressions of geologic processes included in the study know as geomorphology. Please see the web page on the OSA web site entitled Geoarchaeology in Iowa.
Landform Regions of Iowa, 2000
Regional Bedrock Maps and Descriptions
The 1998 bedrock map is also tied to individual regional bedrock maps currently under production by the Iowa Geological Survey. These maps afford a more detailed view of smaller regions and are accompanied by a through review of previous research and current understandings. Insets identify shallowly buried and surface bedrock outcrops.
Bedrock geology of northwest Iowa, Digital geologic map of Iowa, Phase 1: Northwest Iowa, B. J. Witzke, G. A. Ludvigson, R. R. Anderson, B. J. Bunker, M. K. Slaughter, J. D. Giglierano, J. P. Pope, T. M. Whitsett, and M. J. Bounk, 1997, scale 1:250,000; contract completion report to U.S. Geological Survey for Assistance Award No. 1434-HQ-96-AG-01486, August 1997.
Mary De La Garza, Web Master