It was recently pointed out to me that glass was in fact a liquid and not a solid…take stained glass windows in old churches for instance, if you look at them closely, the glass at the bottom of the window is thicker than the glass at the top…granted it takes centuries for it to deform in that way…but I’d just like to know the facts. 
- Any takers?
Well Alior you were not steered in the wrong direction. Glass is in fact in its liquid state, even when we see it in houses and the like, on windows etc…etc… It all has to do with the viscosity of glass…it is very very very slow. The glass is made up of of course of molecules and those molecules are moving at a slightly above static state. They are not a very dynamic force. And when we see glass we are seeing it in its liquid state, all the time… For instance I have lived in housed made in the 19th century, the glass on those windows is visibly distorted. One has to make sure to never run their fingers across the top of this glass or you’ll get cut, because the top is as thin as a razor and the bottom has become fatter, much like a tear drop… Also as far as I know scientists do not know how long it takes glass to decompose, so I guess the questions will still linger…I hope I have answered some of your questions…
ahh, it all becomes clear…my head that is, not the glass 
With all due respect Phlosphr your parody answer to the OP , while amusing, is close enough to what some people believe that it might be taken as fact and cited as such. If you’re going to do this in GQ you might want to have a “just kidding” note at the end of your post.
Right on, Astro.
Unka Cecil does a nice job of debunking the old urban legends about glass.
Um, you were kidding with your answer, weren’t you, Phlo?
Cecil’s answer is close enough, but since both OP and one satirical respondant brought up the old ‘glass is thicker at the bottom because it flows’ factoid, allow me to stress that this is a case of misattributed causation. Floated Glass, which is the method of manufacture for most modern window glass, produces remarkably flat panes. Rolled glass (especially earlier, hand rolled glass) can exhibit a characteristic rippling on the surface, and one edge my become thicker than the other as the glass cools during the process. Being of practical nature, builders almost always placed this thicker edge at the bottom.
Try this explanation on for size:
Whether glass is a liquid depends on how you define “liquid”.
If you mean it seems to sag and run over a time frame you will notice, then glass isn’t - the thickened windows are examples of other causes. Go see 2000 year old Roman glass vases if you want to see something 10x older that hasn’t run at all.
Some people consider Silly Putty a liquid because it runs over the course of hours or days.
Glass is very much slower still, so that for any practical human or historical purpose it is rigid.
But the underlying reason it gets called liquid is that it is not crystalline in its molecular ordering. In many substances, such as most rocks and metals and ceramics, there are tiny regions inside where the atoms and molecules are organized very regularly. These regions can’t change shape unless temperatures or forces get very big. Therefore they have a sort of long term permanance over geological time spans. Other substances are called “amorphous” (“without form”) because there is no crystalline ordering. Liquids and glass are in this category. If you looked at a small enough scale you would probably categorize glass with the liquids, though in our macroscopic experience it is more practical to consider it a rigid solid.
And it is a matter of time scales. If you shoot a projectile into liquid water fast enough, it shatters into jagged sharp shards, just like glass will at lower speeds. You might just say that the time it takes water to demonstrate its runny liquid nature is many orders of magnitude less than the time likewise for glass.
Well if glass is a liquid, then humans are too!
Think for a second…
With age, we get wrinkles, which occurs because there is less collagen in your skin, then our skin moves downward. Now, although our cells aren’t all the same material, the same principle applies.
In that case, cast iron is a liquid too! If you have a HUGE piece of cast iron, balanced on one small little point, that point will be thicker after 100 years than it was when you began the experiment.
This thread contains some very interesting and relevant links on the matter.