the fourth gym is in celadon city at the bottom left of the city.
the gym leader is erika.
the badge is called the rainbow badge
the wake badge
lavaridge gym.
In Diamond, Pearl and Platinum 7th gym is in Snowpoint Town.
In Pokémon Silver, the fourth Badge that you get is the Fog Badge and you will get it after beating Morty, the leader of the Ecruteak Gym.
The fourth Gym is in Lavaridge City on the most western side. The Gym Leader inside is named Flannery and she specializes in Fire-type Pokemon. Her Pokemon are a level 26 Slugma, level 26 Numel, and a level 28 Torkoal. After defeating her, she'll give the TM Overheat with an addition of the Heat Badge for your Badge collection in Hoenn.
the fourth badge is obtained from crasher wake in pastoria city
Cobble badge
you go the the fourth gym in pastora and battle him
The fifth gym is in Hearthome City - you have already been here.
what do you do after beating the fouth gym in pokemon pearl
Beat the gym leader
Snowpoint City.
Veilstone City
The mine badge.
Beat the Gym Leader
Go to the forth gym!
In Diamond, Pearl and Platinum 7th gym is in Snowpoint Town.
By beating the gym leader
The 4th pokemon badge is given by Erika the Celadon City Gym Leader.