And I agree that not all of them are of this nature. I reckon that a lot of petroglyphs are religious, but some must be star/land charts.
In the mean time take a look at this baby
http://www.indigogroup.co.uk/IrishGenius/zBaltynanima.htm
I haven't reached this yet, although it is only about 35 miles from where I live. I would also like to see the others that have been found in the area. The OS reference on this page is wrong and out by about 10 miles. The OS map has it marked but as a bullaun stone. This is certainly no bullaun, but is probably the missing ling between cup & ring and the later bullaun stones.
Maybe I'll go find it over yule when I have some time off.