このふたつは基本的に互換性があると考えていいんじゃ ないかな。例外が思いつかない。個人的な好みでどちら か一方だけを使う人が多いような気がするね。

なるほど。
それ以外に「量る」と「計る」は？Is one more for weights and the other distances and times?

これも実際には普通の人は違いを気にしないと思う。た だ、「辞書的なルール」で言えば、次の事が言えるかな 。

量る　weights & volumes
計る times
測る distances & areas

ありがとう、さしみスターさん

Time for a list of new questions! A great many questions! :)

石、岩、岩石 How are these words different? Is 岩 a different size? Does it sound more like a boulder (I notice there is the mountain radical in the kanji)? Is 岩石 more scientific/literary/technical? It's kango, which is why I was thinking so.

What about:
1. 谷 vs. 渓谷 Is just one more literary/scholarly/scientific?
2. 増す vs. 増える synonyms? They're both native Japanese intransitive verbs meaning "to increase."
3. 分量 and 量
4. 減少する and 減る—is the former just more technical/formal/stiff sounding?
5. 省みる and 反省する—same as in #4?
6. 空の and 空っぽの for "empty"—how are they different? The latter sounds "cute" or very conversational to my ear.
7. 固い／堅い／硬い—This can be passed upon. I know it's a bit tougher, and reading the Japanese explanations made it difficult. I think the first is a bit more like "unchanging" like being stubborn or something.
8. バス停／停留所—Is the latter just more like what you'd see in a journal article or something more technical?

Umm.. I will add my two cents on some of these, which probably will not help you, or is wrong.. but here goes. 岩 vs　石 my impression has always been that 岩 has the connotation of being bigger than 石 or a least more mountainy or something.. Like I don't think you could say 池に岩を投げる.. I mean maybe you could but it would portray a different image than what people normally think of.. I think..

増す vs 増える.. .I am pretty sure 増す is transitive.. and 増える is intransitve.. when　が　is used with 増す i think it is just a subject marker. For me when I use を.. I use 増す.. and I would never use を with 増える。

and last one I will comment on　空の vs　空っぽの.. I have typically said 空っぽの when talking about somebody's empty brainless head, but the exact difference.. just wait for a native..

No, I think they are both intransitive. Maybe you're misreading the first as 増（ふ）やす rather than 増（ま）す? Because 増やす is transitive. 増す is not, as far as my book is concerned. Or, at least, maybe the latter can be transitive and intransitive. In Eijiro, it indicates masu as 【他動】, which means it is intransitive. But it also has 【自動】 examples as well. As an intransitive it means "to add," which is the meaning I'm curious about. As a transitive, it means "heighten/intensify/rise." But that's weird because "rise" is intransitive!

But thanks for the input!

Today has been very productive. My favorite new word is 系列子会社 (subsidiary company)!

I checked my dictionary, and it actually has 増す　（ます） as both transitive and intransitive... interesting.. it has an example sentence of 速度を増す and 彼女の怒りが増した。　Haha, I salute your desire to figure all this stuff out, but questions like these always just gave me headaches.. so I usually avoid them like the plague.

Well, while I'm in between jobs, I'm making a heavy push for JLPT1 success. :)

石、岩、岩石 How are these words different? Is 岩 a different size? Does it sound more like a boulder (I notice there is the mountain radical in the kanji)? Is 岩石 more scientific/literary/technical? It's kango, which is why I was thinking so.

石 any small stone/rock you find on the street, in the school yard, in the park, etc.
岩 we usually use this to refer to a larger stone in the mountains or by a river.
岩石 is our usual kango for scientific/technical use.

What about:
1. 谷 vs. 渓谷 Is just one more literary/scholarly/scientific?
Exactly.
2. 増す vs. 増える synonyms? They're both native Japanese intransitive verbs meaning "to increase."
As has been answered, the former is both trans. and intrans. When it's used as an intransitive verb, it sounds less casual than 増える.
3. 分量 and 量
Generally interchangeable. 量 tends to sound a bit more scientific than 分量, but most of us couldn't care less.
4. 減少する and 減る—is the former just more technical/formal/stiff sounding?
Precisely.
5. 省みる and 反省する—same as in #4?
Classical case of Yamato vs. Kango.
6. 空の and 空っぽの for "empty"—how are they different? The latter sounds "cute" or very conversational to my ear.
You're acquiring a Japanese ear. Latter can sound pretty childish even though many adults use it.
7. 固い／堅い／硬い—This can be passed upon. I know it's a bit tougher, and reading the Japanese explanations made it difficult. I think the first is a bit more like "unchanging" like being stubborn or something.
This isn't very simple. I'll sleep on it.
8. バス停／停留所—Is the latter just more like what you'd see in a journal article or something more technical?
Former is the usual choice. Latter carries a somewhat poetic overtone.