Red to light brown soil is well drained, while darker soils are more poorly drained. Spots of color indicate a fluctuating water table. Sandy soils dry quickly and hold less nutrients. Silt and clay soils hold too much water and plenty of nutrients. A loamy will knead like dough in your hand.
Sandy soils are gritty.
A deep soil allows for deep roots. Trees with deeper roots are more windfirm and more drought resistant. The dark, mucky, organic layer is what we walk on. This is indicative of a well drained soil, having good aeration, and plenty of soil-mixing earthworms. Keep in mind that soils change over short distances because of changes in topography, slope, aspect, vegetation, and fallen trees.