I don't know what "the singers" are, but someone must know. The shape (of the opening) is so of its own, that I estimate it to be known (already). I've seen such things somewhere ealier. In books, maps, or in stone-pictures. It's part of the proof... that thing.
(Hmm... there are also certain standing singers ... with collars ...)
The black lines may be roads, but they are built on ready lines, that were long charnias, one after another. There are things to study, about very long charnias being as zippers of kilometres and dozens of kilometres long sacks... Were they hunters or unselfish water-pipe-builders ( <-- not totally crazy thought: community's parts can specialize and work for common wellfare. The complex would control parts.), or organisms that lived on the riversacks... and was there always "a sack-river" with those... Sacks were without those. Many organisms are in some sacks, together. For some mysterious reason. Did they go together when were in trouble, and maybe made some slime, that made those sacks on them? It may be reproduction... (I repeat myself) - something may have happened inside the sacks, and out crawled only 1 or few big creatures... bigger than their several parents.
Before I got my other computer totally black & stuck, I made this study about a local, ~1,5m stone:
