Silty sand is denoted by the symbol "SM" in the soil classification system.

Explanation:
Soil classification is a system used to categorize and describe different types of soils based on their physical properties. The system helps engineers and scientists understand the behavior of soils and make informed decisions regarding construction and land use.

The soil classification system used in the question is based on the Unified Soil Classification System (USCS), which was developed by the U.S. Army Corps of Engineers. This system classifies soils into different groups based on their grain size, plasticity, and compressibility.

In the USCS, soils are classified into three primary groups: sands (S), silts (M), and clays (C). Each group is further divided into subgroups based on their specific characteristics.

Sands are coarse-grained soils with particle sizes ranging from 0.05 mm to 2.0 mm. They are further classified based on their grain size distribution and the presence of fines (particles smaller than 0.075 mm). For example, sand with fines is denoted by the symbol "SP", where "S" represents sand and "P" indicates the presence of fines.

Silts are fine-grained soils with particle sizes ranging from 0.002 mm to 0.05 mm. They are characterized by their smooth texture and ability to retain water. Silty soils are denoted by the symbol "M".

When sand and silt are combined, the resulting soil is known as silty sand. Silty sand has a higher percentage of sand particles compared to silt particles. Therefore, it is classified as a subgroup of sand, denoted by the symbol "SM". The "S" represents the presence of sand, and the "M" indicates the presence of silty particles.

In summary, silty sand is denoted by the symbol "SM" in the soil classification system. This classification indicates that the soil contains a significant amount of sand particles along with some silty particles.