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Service Description: This is a polygon feature class containing driftless areas in Illinois. These areas are analogous to areas of the state where the bedrock surface is not buried. Data are originally from the Buried Bedrock Surface map (1:500,000) by Herzog et al (1994) and the related feature class Bedrock_Topography_1994_Ln. There are no attribute data associated with the spatial data in this data set. The nominal scale is 1:500,000. Several major bedrock valleys are found across the state. The greatest control for the present bedrock surface configuration was probably the preglacial surface configuration. Interpretations of bedrock topography have been modified since the 1950's. Horberg contoured his map with the philosophy that the bedrock surface map represented the preglacial topography modified by glacial erosion, which formed U-shaped valleys. The current map, showing narrow valley channels and bedrock knobs in wide channels, indicates complex preglacial and glacial erosion primarily from running water. The major valleys were formed before the minor valleys that appear as tributaries. Streams that formed during successive glaciations probably eroded to bedrock and produced the small tributary valleys to the main channels. The bedrock surface was less likely to be eroded as sediments accumulated during each successive glaciation. Please refer to the metadata for the parent coverage, Buried Bedrock Surface of Illinois for more information.

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• Driftless Areas (0)

Description: This is a polygon feature class containing driftless areas in Illinois. These areas are analogous to areas of the state where the bedrock surface is not buried. Data are originally from the Buried Bedrock Surface map (1:500,000) by Herzog et al (1994) and the related feature class Bedrock_Topography_1994_Ln. There are no attribute data associated with the spatial data in this data set. The nominal scale is 1:500,000. Several major bedrock valleys are found across the state. The greatest control for the present bedrock surface configuration was probably the preglacial surface configuration. Interpretations of bedrock topography have been modified since the 1950's. Horberg contoured his map with the philosophy that the bedrock surface map represented the preglacial topography modified by glacial erosion, which formed U-shaped valleys. The current map, showing narrow valley channels and bedrock knobs in wide channels, indicates complex preglacial and glacial erosion primarily from running water. The major valleys were formed before the minor valleys that appear as tributaries. Streams that formed during successive glaciations probably eroded to bedrock and produced the small tributary valleys to the main channels. The bedrock surface was less likely to be eroded as sediments accumulated during each successive glaciation. Please refer to the metadata for the parent coverage, Buried Bedrock Surface of Illinois for more information.

Copyright Text: Illinois State Geological Survey

Spatial Reference: 102100  (3857)


Initial Extent:

XMin: -1.0325695304060021E7
YMin: 4414983.498513765
XMax: -9587099.679533279
YMax: 5276972.186803925
Spatial Reference: 102100  (3857)

Full Extent:

XMin: -1.0109521485959249E7
YMin: 4454165.765369087
XMax: -9803274.856815238
YMax: 5237792.081305312
Spatial Reference: 102100  (3857)

Units: esriMeters

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Title: Layers
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Comments: This is a polygon feature class containing driftless areas in Illinois. These areas are analogous to areas of the state where the bedrock surface is not buried. Data are originally from the Buried Bedrock Surface map (1:500,000) by Herzog et al (1994) and the related feature class Bedrock_Topography_1994_Ln. There are no attribute data associated with the spatial data in this data set. The nominal scale is 1:500,000. Several major bedrock valleys are found across the state. The greatest control for the present bedrock surface configuration was probably the preglacial surface configuration. Interpretations of bedrock topography have been modified since the 1950's. Horberg contoured his map with the philosophy that the bedrock surface map represented the preglacial topography modified by glacial erosion, which formed U-shaped valleys. The current map, showing narrow valley channels and bedrock knobs in wide channels, indicates complex preglacial and glacial erosion primarily from running water. The major valleys were formed before the minor valleys that appear as tributaries. Streams that formed during successive glaciations probably eroded to bedrock and produced the small tributary valleys to the main channels. The bedrock surface was less likely to be eroded as sediments accumulated during each successive glaciation. Please refer to the metadata for the parent coverage, Buried Bedrock Surface of Illinois for more information.
Subject: Driftless Areas in Illinois
Category:
Keywords: geology,bedrock,driftless,drift,glacial,surface,surficial,Illinois
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Enable Z Defaults: false

Supports ApplyEdits With Global Ids: false

Support True Curves : true

Only Allow TrueCurve Updates By TrueCurveClients : true

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Supports Dynamic Layers: false

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