Is there any way to delete/cancel any of your additional or secondary Tumblelogs?.  Indeed, following the steps below will give you the info required to cancel/delete/erase a secondary/alternative Tumblelog on Tumblr.

How to Delete a Secondary Blog on Tumblr.

1. In your dashboard, looking your sidebar you will see the title of you main blog, and right next to it a drop down menu, click on it and choose the secondary tumblelog that you want to delete.
2. Once in your secondary blog’s dashboard, there will be a new option right under the blog’s name in the sidedar (same place as in the first step).  The link is called Members. click on it.
3. You will be taken to another screen, there’s an option called Leave This Blog, if you are the only member of this blog, it will get deleted after you confirm this step.