Some suggest a variant of「array sliding down」from「orifice」as a hole created in the rock ceiling above within the old caverns, or rocks that have fallen from above the orifice entrance hole to a cavern, but frankly, this would have occurred while being witnessed by humans how many times? Not many folks would stay long near a cave that is crumbling rapidly (do caves ever crumble rapidly?)…both of these scenarios are far-fetched and highly unlikely, given that they would occur so seldom if at all during a human lifetime. Sometimes humans lack an appreciation of just how long the Earth's rocks have been around and how stable rocks really are:「If we looked at Earth's creation through a clock measuring a 24 hour time span…. Humans would have appeared」at 23:58:43, or stated another way, the entirely of human existence would fit into a time slot of 77 seconds….
[ https://blog.onlineclock.net/24-hour-history-of-earth/ 2015-03-09 ]
In any case, the simple elemental meanings as used throughout these glyphs make the most sense:「arrayed, horizontal motion」of「erection or head with an orifice」clearly describes that the only portion still visible are the ROCKS, STONES held within the scrotal sac, and not coincidentally traditional Chinese fonts depict the elements drawn as「horizontal motion」of「person standing」with「in-and-out side-to-side.」MINERALS are the fundamental building blocks of nutrition and all life, and spermatozoa originates in the testes, or ROCKS (see「life」生). And, lest we forget, ROCKS first appeared above the surface of the ocean fluids due to molten LAVA spewing from LAVA cones (see「rod within cavity」山). Literal rocks seldom rock in a 'rocking motion' apart from the soil, being highly stable, fixed, and heavy, but testicles in a scrotum are rocking and rolling almost constantly the world over…think about it: how often have you seen literal stones naturally in a 'rocking motion'? never—gravity and inertia do not allow for that, other than perhaps for a few moments of a highly unusual, delicately balanced rock during an occasional earthquake.

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: rock; stone; stone inscription; one of the eight ancient musical instruments 八音; dry measure for grain equal to ten dou 斗; ten pecks; one hundred liters
Japanese EDRDG: stone
Unihan extended: stone, rock, mineral

Used within names (nanori)
いさ　･　いす　･　いわ　･　し　･　せっく　･　と