i went over to friends place the other day and we were looking at his guns and he pulled one out of the cabinet it was an 1894 marlin in 38-40 the serial number 1239 anybody got a book on them that can give me a idea of when it was made it would appreciated thanks

It sounds more like an 1889 model. Read mon:
The 1889 was made from that year until around 1903. Brophy says a little over 55,000 of them were produced. In 1894 there were 4498 made & of the total production, 18641 were in 38-40. 106XXX shows 1894. Be cautious with what you feed it, as the action is not overly strong. Jacketed bullets should be avoided. SW
marlin-collectors.com
i went over to friends place the other day and we were looking at his guns and he pulled one out of the cabinet it was an 1894 marlin in 38-40 the serial number 1239 anybody got a book on them that can give me a idea of when it was made it would appreciated thanks

What you have is a Model '94. The 4 digit serial number should have a letter prefix. Sometime after WWI, Marlin started with the new numbering system. There are some people at marlinowners.com that would be able to give you a closer date as to when it was built.