Pure mineral magnesium silicates are amongst the most difficult substances to decompose by naturally occurring agents. Pure water exerts no chemical action on them, neither does water containing carbonic acid gas, even although the latter body be present to the point of saturation. Fresh spring, river, or lake waters containing alkaline carbonates in solution are also, as my experiments prove, totally unable to decompose pure natural silicate of magnesia. Of course, it must be remembered that the amount of alkaline carbonate in natural waters is very small.