I mean, I know I can scroll forever, but is there a better way?
Oh, and while I’m asking, is there a way to mark a thread read without scrolling through it all? I’m hopelessly behind on a few because of the end of the term, and need to declare bankruptcy and start over.
There totally is!!
Do you see a tiny little thin blue line on the side of threads with many replies? It’s a little scroll bar and will pop up with the number of replies on that thread. You can drag it up and down. 
Let me know if that … didn’t make sense…
This!
If you click on the 13 unread under your suggestions, you can then dismiss them
Bankruptcy achieved, thanks! That fixed both my problems at once.
Ooh, options!
Edit: but I can’t figure that one out. Maybe it doesn’t work from a tablet, will try later from computer/phone and report back.