Is it usual for a PhD thesis to have two distinct subjects? In my PhD studies I have slipped off my original track of research. This was also caused by the fact that I found out that my work can be generalized to a broader scope. It is not so bad, during this detour I did a lot of work.

But then I tried to get back to my original subject and did a lot of work there too. So now after 3 years of studying, I have several papers and a lot of data for both tracks. I don't think that the results in any one of these tracks are sufficient to graduate, but together they are.

Should I:


try to find a unifying theme and try to make my thesis seem unified on the outside, or 
should I transparently say that my thesis is about these two subjects?
Option 1. At least in computer science, it happens often (but not always) that someone works on several somewhat disjoint but somewhat related problems. It's all about the glue and the story; if you can sell the cohesiveness of the thesis in the abstract and introduction, you're golden. Be upfront about the fact that there may be some disjoint problems, but try to find and highlight the unifying themes. 

Here's a quote my advisor always tells us which has relevance to this: "all wells, when dug deep enough, lead to the same water source."