So we are running a bible study exercise in the local assembly I belong to and serve in and it's been really really like I have not read the bible before.

A few things that jumped at me... in genesis during creation you see ...

"After his kind, after their kind"

"Lamech saying he slaid a man, and if Cain was avenged seven fold then him seventy fold" who did he slay.. and what a trend of blood.. 

where did Cain meet his wife...his sister? prolly not spoken about. A couple of silent things...

I guess you also had those questions, but I remembered again that whatever the scripture leaves out might be something not needed for our salvation and if those lines needs to be filled it would be for our salvation and it would come by revelation. So, there is safety in wisdom.