unfounded

Having no strong foundation; not based on solid reasons or facts.

an unfounded report; unfounded fears

[…] my chiefest design ever since the seventeenth year of my age […] consisted in elaborating such demonstrations in Natural Philosophy, as might serve to unfold the natures of Beings in relation to the Art of Physick, hitherto so uncertain, blind, and unfounded on Art […]

Not having been founded or instituted.

Even the great world as yet undiscovered, the cities as yet unfounded, and the history as yet unwritten, are lost: fallen from the beginning.

Bottomless.

[…] from them I go This uncouth errand sole, and one for all My self expose, with lonely steps to tread Th’ unfounded deep […]

He makes this Glob so spacious and fair Unfix’d, unprop’d, unfounded any where, Hang, like a Water-bubble in the Air.