What is the name of the soil that is crumbly dark brown and is a mixture of humus clay and other minerals?

The soil you are describing is likely "loam." Loam is a well-balanced mixture of sand, silt, clay, and organic matter (humus) that is known for its crumbly texture and fertility. This type of soil is highly regarded for gardening and agriculture due to its ability to retain moisture while providing good drainage and nutrient availability.