Death valley is this desert plain, a dry lake bed in California surrounded by mountains and on the desert floor these huge rocks, some of them hundreds of pounds.这是托福TPO4听力中的一段话，其中on the desert floor these huge rocks感觉不通顺，没谓语或者非谓语，these huge rocks是当同位语理解吗？
and on the desert floor these huge rocks, some of them hundreds of pounds.
在 and 之后，黑体部分是并列分句，some of them hundreds of pounds 是是这个并列分句的 “独立主格结构”。该分句其实是省略了 谓语动词 are 。on the desert floor 不可能作定语，介词短语作定语是没办法前置的。
on the desert floor these huge rocks, some of them hundreds of pounds.
从语义上剖析，死亡谷是沙漠平原，可以被群山环绕，不可能被沙漠底部巨大的岩石环绕。第二个并列分句的意思是：“沙漠底部有巨大的岩石，其中有的重达数百磅。”
