Surface Materials Map of surface materials reproduced from Appendix 1 on page 159 of “Exploring Stone Walls.” Samples of stones from different map units shown below. Map unit “Sand & Gravel” (ORANGE) consists of stones rounded by subglacial milling and meltwater transport. Hope Ontario. Map unit “Moraines” (BLACK) consists of a great variety of material, generally a containing a mixture of stone shapes and sizes. Montauk Point, Long Island. Map unit “Fines” (PINK) consist of clay-, silt- and sand-rich lake and marine sediments without surface stones. They are present at great depth. Map unit “Shallow Bedrock” (BLUE) is usually ledge overlain by rubble or hardpan. Bethel, ME. Link back to stone wall provinces.