Proper mortar mix for re-pointing field stone foundation.?

What would be the proper mortar mix for a field stone foundation. The old mortar is crumbling and turning to sand. Some people have said to use quikrete type N mortar mix, while other people have said not to use it because it contains portland cement. Has anyone used this before in their field stone foundations? I... show more What would be the proper mortar mix for a field stone foundation. The old mortar is crumbling and turning to sand. Some people have said to use quikrete type N mortar mix, while other people have said not to use it because it contains portland cement. Has anyone used this before in their field stone foundations? I just don't want to cause any issues with the foundation. I assume there was originally lime in the mortar which type N has, but someone mentioned that since there is portland cement it may not handle water and moisture as well when it comes to drying out.

This seems like a typical field stone foundation you would find in the Northeast in terms of rocks that were used.
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