I WOULD inform the authorities. They can send out a warning to the public that a dangerous substance is being sold as LSD, with a clear description of the blotter or pill.

The public needs to be warned as quickly as possible before any serious accidents will happen.

If possible, i would sent a sample to the most apropriate institution so they can test what exactly is in it and how much.

Your dealer isn't personally responsible since he has bought the stuff from yet another one. If your dealer is not a very bad guy, i would also inform him and urge him to throw the stuff away.