Some mossy mineral(chloride?) grew a stalactite from the roof of the water-filled cavity before being coated with agate.

-#1 is regular agate layers that were deposited when saturated & colored solutions entered the cavity and each layer may represent a single season or a wet period (monsoon rains, or fluctuating levels of a nearby river/lake). Note the gray bands suffer from the lack of impurities needed to give those layers some colors.
-#2 is "Waterline" agate where the solution got oversaturated that silica was deposited very quickly (same for opals too). So it's obvious that there was a change in enviroment where excess silica was provided.
-#3 is quartz crystals where the solution got undersaturated (too much water, not enough silica) and such undersaturation allowed the quartz molecules some time and room to organize themselves into crystals. Another example of a change in enviroment.
    Now the most interesting thing about this specimen is that #1, #2 & #3 sequence was repeated as if the climate was
oscillating. (shifting back and forth) all the way to the channel itself. The second agate layer is almost colorless as if there are no more mineral impurities to spare.
    When did the agates start growing? That question will never be answered, because we have no way of knowing. We can find out the age of the volcano rocks by carefully analyzing several different specific mineral that act as "clock timers" that tell us how many millions of years have passed, and being formed from solutions, the agates don't have such impurities. Take Lake Superior Agates for example, Lake Superior Agates were said to be oldest agates known mainly because they came from a billion years old lava beds around Lake Superior. But the problem is that we have no idea of WHEN did those those Lake Superior Agates started forming even we're getting hints from a variety of silica called moganite intergrown between the fibers of agates that decay over time.