The Digital Geological Survey of Illinois contains 4,451 text pages, 7 fold-outs, 276 plates, 3 color foldouts and one very oversize map. Pages (including foldouts and map) were scanned to create 1:1 page images. All text pages and all text pages that describe plate pages were scanned at 1-bit, 600 spi, and saved as TIFF 6.0 files compressed with ITU Group 4 compression. All plate pages were scanned at 8-bit grayscale, 600 spi, and saved as TIFF 6.0 uncompressed files. All color pages were scanned at 24-bit, 600 spi and saved as TIFF 6.0 uncompressed files.