Can anyone identify one or more horror movies I watched around 1973?  They were old then, 1950 - 1965.  I can't say whether black-and-white or color as the sets on which I saw them were black-and-white and I am not sure whether all the scenes I recall are from the same film.

The one I most want to remember had some features in common with The Blob and with the short stories "It" by Theodore Sturgeon and "Slime" by J. P. (Joseph Payne) Brennan.  I checked film credits for both Sturgeon and Brennan and this film is not an adaptation of either story.  I am also quite sure it is not The Blob as I saw much of that recently and the ending in particular is completely different.

In this film, a huge rolling mass of sentient slime attacks a small rural probably Southern American community.  This is not humanoid slime but in form more like the Blob but as I recall in appearance more like liver than raspberry preserve.  There is something about a cave--I believe the slime originally oozes from there.  There might be something about a guy trying to attack it with fire, or someone attacking him mistaking him for the slime monster, as there is a scene of a guy running from the cave screaming on fire from head to foot, who was not the monster but an innocent victim, either a mentally challenged man who hid out in the cave or someone who went there to combat the monster.  This greatly upset me as a child.  A little boy may or may not have been shot.  In one scene, a lady with a distinct rural Southern American twang says how awful and horrible it was that "they shot that little boy," but I don't know whether a boy was actually shot or she just thought one was, or whether he was fatally shot or just wounded.

Naturally for much of the film, the monster is unstoppable.  It is chased by military personnel with automatic weapons, tanks, etc.  Towards the end it becomes entangled in a barbed wire fence and just sort of falls apart or dries up or is shot to pieces or all of the above.  Anyhow, it dies or is destroyed or wherever slime monsters go.

What started this whole line of inquiry is some dude posted on the Ray Bradbury Message Board that he read this Bradbury story, again basically about sentient slime--a wad of pond scum, sticks, and the like, takes on physical form, wreaks some sort of havoc, and at the end dissolves at the bottom of a flowing stream.  Three of us (Bradbury board members) told him we have read every well-known story by Bradbury and a good many rare and lesser known works, and Bradbury wrote no such story!  One person said it was "It" by Theodore Sturgeon, which made me remember that in 1977-1978 I read that and another story I believe must have been "Slime" (though I can find neither story online and have none of the anthologies in which they are listed nor can I even identify where I may have read "It,") and the stories reminded me of this movie I saw on a pay TV at a bus station in 1973 and also the same film or one like it ran on TV, both before I read these stories.  Anyhow, the dude INSISTS this is NOT a mistaken attribution because there was a little afterward in the book, asking the author why he wrote such a horror story and how it made him feel and he said he felt "cleansed" at the end which is "classic Bradbury" (which maybe it is but Bradbury did not write this).  So anyway I emailed the Sturgeon trust official who is Sturgeon's daughter and asked if she can identify anthologies in which "It" appears not listed in the Locus Index to Science Fiction, as I recognize none of those, and it's not in any of the books I thought it was.  I'm getting a bit irked because I spent a good deal of time today checking anthology contents and story summaries and am now bound to turn up where I read the story, if indeed I did, or how wrong my memory is if I did not, and in any case prove that sucker wrong!

Here is a much more complete bibliography for appearances of "It" than in the Locus List, from which I find I do have at least one book containing the story:  http://www.isfdb.org/cgi-bin/title.cgi?41269

Here is a list for appearances of "Slime," which I seem to have read in Alfred Hitchcock's Monster Museum along with my very first Ray Bradbury story, "Homecoming":  http://www.isfdb.org/cgi-bin/title.cgi?88069

Solved the OP's question and posted the following.  Still have my movie questions.

And the winner is...Richard!

The story is indeed "It" by Theodore Sturgeon.  The description of the monster melting in the water is found near the end.  It is rather lengthy and I could find no preview giving the entire quote though I searched both Amazon's Sturgeon page and Google Books at length.

I hope you're happy now that I spent hours on this today.  The correct story and notes on it can be found, among other places, in The Ultimate Egoist:  Volume I:  The Complete Stories of Theodore Sturgeon.  This is Book 1 of 13 in the Complete Stories of Theodore Sturgeon Series.  One of the Forewords is written by Ray Bradbury which should explain any confusion.

Here is a screenshot of part of the story notes which should settle this once and for all.