That's a nice Burt bottle Pontilguy. The CSB on the back stands for Crystal Spring Brewery.
John Burt also used ponies, tall blob tops and hutches before his sons took over the brewery in the 1880s. The hutch is his rarest bottle. I've been looking for one for about 15 years now!
The CSB on the back stands for Crystal Spring Brewery. There are also squats that say CSB EAST STROUDSBURG PA on the front with blank reverses and there's the elusive CSB EAST STROUDSBURY PA misspelled variant. That's a cool one too.
John Burt appears to have been involved with the brewery from the day it opened so I've often wondered why there are bottles with and bottles without his name. They must have been used at the same time...