lsd can last up to 10 hours, mescaline lasts up to 8 hours maximum.

both are safe if taken in reasonable doses.

you can tell the difference bythe amount of powder neccessary for a significant dose of mescaline is typically more than what's contained in a "microdot" or other small pills touted as mescaline. Mescaline is active in the 200+ milligram range and requires a normal sized gelcap or large sized pressed pill to contain this much material. A common dose of LSD is 100-200 micrograms which can easily fit in a small tablet. also lsd is likely to come on blotter paper and to my knowledge mescaline does not.

effects are pretty similar to each other, check out erowid.org for more info