I take both geography and chemistry at a-level. Chemistry takes a lot of time to get your head around most of the concepts, but geography you have to spend a lot of time learning the case studies.
If you want to go into science, definitely take chemistry. Although most geology, environmental sciences and geography courses like you to have geography and will accept maths as your science, if they haven't already said that geography counts as the science. Most universities like students with geography at a-level, because it teaches the key skills needed at university. You spend a lot of time on research techniques and sourcing, which you will most definitely need, no matter what subject you take.
Personally, I spend a lot of time on chemistry, because I know I need to, where geography I put very little time in to. I write my case studies on flash cards and only look at them a couple of days before the exam, and I get the grades I need. This will not be the same for anyone, but you can compare how much work you did at GCSE and see the results you get. I got a B in GCSE Chemistry and did not even have a teacher for a year, but put a bit of work in and motivated myself. I really cared what I got in geography and panicked a lot about it, so now I know my abilities in the subject, I am a lot more laid back with geography, where I am still trying to prove myself to my teachers in chemistry.
Overall, I think the step up between GCSE to A-level is a lot smaller in geography, and you mainly cover the same things anyway, so it was a lot easier this year, in my opinion. If you are that stuck on deciding, have you tried speaking to both your geography and chemistry teacher and explaining your situation?
Also, if you take geography at university you could go into many jobs, so do not worry about that. For example: teaching secondary, university lecturer, PhD in it, research scientist in a university, Environmental Agency, Defra, the council, British Geological Survey, USGS or the ones in any other country.