1. He was sitting on a rock.

2. He was sitting on many rocks.
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Was he sitting on a large piece of stone or on small stones?
In American English, 'rock' means 'a small stone' or 'a stone of any size'? Is it right?
In British English, a rock is usually a large piece of stone, isn't it?

Rocks and boulders are generally thought of as being much larger than stones.

http://www.google.com/search?q=difference+between+rocks+and+stones&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiZhv---KnTAhUE4mMKHcMqCwoQ_AUIBygC&biw=1366&bih=638

1. Based on the statement "He was sitting on a rock," it is not specified whether the rock is large or small. The size of the rock is not mentioned.

2. Similarly, in the statement "He was sitting on many rocks," the size of the rocks is not specified. It could refer to many small stones or a combination of small and large rocks.

Regarding the usage of the word "rock" in American and British English, it is important to note that language usage can vary. In general, "rock" can refer to both large and small stones in American English. It can be used to describe anything from small pebbles to larger, more substantial stones.

In British English, "rock" typically refers to a larger piece of stone. It is more commonly used to describe a substantial mass of stone, such as a large boulder or a rocky outcrop.

However, it's important to note that the word "rock" can have different meanings and contexts in various situations and regions, so it's always better to consider the specific context or ask for clarification if needed.

1. In both American and British English, the word "rock" can have different meanings depending on the context.

2. Generally, in American English, the term "rock" is often used to describe a smaller stone, pebble, or any stone of various sizes. So when you say "He was sitting on a rock," it could refer to sitting on a smaller stone.

3. On the other hand, in British English, the word "rock" typically refers to a larger piece of stone, often considered a geological formation or a larger rock structure. So when you say "He was sitting on a rock," it would likely imply sitting on a larger piece of stone or rock formation.

4. To determine if the person was sitting on a large piece of stone or many smaller stones, we need more context. If you have a picture or more detailed description, it would help clarify the size of the rocks. Alternatively, you can ask for more specific information to gain a better understanding.