The formation processes of clathrate hydrate in porous glass powder saturated with a THF-water mixture were directly observed using directional cooling apparatus. As the cooling rate decreased, the THF hydrate grew while excluding glass particles and formed a lens like layer of hydrate in the same manner as in the phenomenon of ice lens formation in the freezing of soil. The growth rate of the hydrate lens was proportional to the degree of supercooling of the growth surface and was about 1/20th the growth rate of the hydrate layer in a THF-water mixture without glass particles. When sodium chloride was added to the system, the growth of the hydrate lens was inhibited depending on the salt concentration.