How do I get google to point to my site map?

I am using my Google webmaster tools - I am currently struggling to see how I can point Google to the site's sitemap.

Squarespace tells me that my sitemap is here: http://yourdomain.squarespace.com/sitemap.xml

However, Google only allows my to search for the sitemap like so: http://www.mydomain.co.uk/

So, is there any way to get Google to see the sitemap?

Thanks,

Mike