Thermal Emission Spectrometer (TES) data from the Mars Global Surveyor (MCS) are used to determine compositions and distributions of martian low-albedo regions. Two surface spectral signatures are identified from Low-albedo regions. Comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass. The distribution of the two compositions is split roughly along the planetary dichotomy, The basaltic composition is confined to older surfaces, and the more silicic composition is concentrated in the younger northern plains.