This is a drylaid rock wall. It is a gravity wall. You can notice the biggest stones in the lower or bottom courses. There is drainage behind it. The rock used is an indigenous sand stone found commonly in Bellingham WA. I do bot recommend this found stone as it does decompose. On this particular project we discussed the pros and cons of this stone. The Owners made the final decision on the type of stone used. It is important to know that some rock types decompose. Thanks for asking, Misty