Which gives more salary ?(civil engineering or mechanical engineering)

It depends on the education level, country, and many other factors, but according to the US Labor Dept, they earned about the same in 2008.
Here's a list from another US group of employers for median salaries in 2009:
Petroleum $83,121
Chemical 64,902
Mining/Mineral 64,404
Computer 61,738
Nuclear 61,610
Electrical/electronics and communications 60,125
Mechanical 58,766
Industrial/manufacturing 58,358
Materials 57,349
Aerospace/aeronautical/astronautical 56,311
Agricultural 54,352
Bioengineering and biomedical 54,158
Civil 52,048

Read the US Dept of Labor/Bureau of Labor Statistics for more interesting facts about the future, which claim that civil engineers will be more needed down the road.

I'm an ME by training and my wife is a CE, and from our experience I agree with the general statement that MEs make a bit more than CEs. At least this seems true in the US. However once you are established in a career then factors such as the specific type of work you do, whether you move into management, and the type of company you work for are important. Many engineers who work for larger corporations tend to have a career path that takes them away from pure ME or CE work even if they don't go into management - it's common to end up in other areas such as systems engineering, quality assurance, product management, or even HR.