Strange, yesterday I found my chickens pecking at some stuff.
I investigated and found....... several blobs of completely clear
jelly, each one about an inch and a half.

Seriously? That's exactly what I have - completely clear jelly, each an
inch or so in size, just sitting there on the soil surface. The only thing
I can think of is water retaining crystals that have somehow mysteriously
found their way onto the soil (although I only use them in hanging baskets
and haven't used them at all this year).

Wind and (later) prolonged rain?

I remember being astounded, last year, by the size and appearance of
blobs like this on a lawn I'd sown using the phb[?] Lawn in a Bucket,
which contains seed, fertiliser and crystals all mixed up together. The
gel blobs didn't appear until weeks after I'd sown it, and we'd had a
lot of rain. Maybe you have a neighbour who's used such a product?