The Shir is a beast of burden.

In their youth they are diminutive, shapeless fleshy blossom-forms, drifting and filtering the lightless and grim under-flows of the Great Lower Sea.

It is in this still unformed, latter quarter of their youth that they are sought out and harvested by Innulian fishmongers. 

Who often risk life and soul to plumb the viscous, somber layers. Blind and naked, and with only a drift-hook bound to their bellies.

To bear hateful light of any measure into the soupy, lurid abyss is to court unspeakable ends. 

So they plunge into the unseeing syrupy salt-wastes with no more than their near preternatural sense of peril to guide.

When by good fortune a youthful Shir flesh-blossom is snared, it is then coaxed into a box-mould of ensorcelled glass. 

Here it will increase, slowly, sometimes over centuries, outstripping many masters, assiduously shaping itself to its confining prison. As the creature ages, its glassy gaol will stretch and yield to its ever burgeoning volume.

When a Shir after many years, at last arrives at a particular mass, its prison-box is leashed to the steam-house in the belly of an undergalley. 

Here its ceaseless tidal to and fro motion against the uncanny glass of its receptacle will produce a terrible heat. Sufficient to drive the undergalley, enveloped by great plumes of salt-perfumed steam, with a reliable swiftness across the viscous lower-tides.