WELCOME TO THE FORUM seems your missing a step, you've dug the hole but now you need to rake up as much as you can this is tedious but critical , Then you want to use a hand compactor and knock the surface rocks back into the dirt.
Now fortunately your rock is rounded and not sharp and there realy isn't that much. But what you do seem to have a lot of is roots. These can be just as bad as rocks if not worse. Rocks don't grow, though they can move from being pushed around by frost and rains. Tree roots can grow right through fabrics and liners with ease. Cutting back the roots are critical. The easiest way to do this is to over dig the excavation and then back fill with sand. The alternative is to use a sawsall, pruners or shears and cut them back into the dirt as best you can.
lastly there are different grades of geotextile and different products that you can use as underlayment. Some have used old carpeting, cardboard, rags old towels and sand. Non woven needle punch geo fabric is the most popular for many reasons and the most common is is that you can get a box store standard of about a 4 oz " not recommended for anything other than soils with very few rounded rocks to 8 oz which is very tough and can keep sharp objects from getting to the liner. to give you an idea how sturdy 8 oz is . you will notice a utility blade dulling and leaving you looking for a fresh sharp edge after only cutting about 40 lineal feet.
