Contains, yes, not “is primarily”, which is what you’re after for pottery. “Is primarily clay and rocks” describes the soil anywhere near me, except with the creeks and rivers where there is more sand.
Now I have found the right pages for those citations:
Influx of people: (what we have is a four-fold increase in the number of settlements over ~60 years) and 60 years seems enough to start producing pottery.
Finklestein, 1988-9. Tel Aviv 15-16 117-183
Zertal, 1991. Biblical Archeology Review 17(5) 28-49; 75
are two of those cited.
The layers from 1280-900 BC are gone; there is plenty from before 1400 BC.
Bienkowski, 1986. Jericho in the Late Bronze Age (Warminster: Aris & Phillips, 1986)
is cited as covering the relevant material.