这段话出自《新概念英语》第四册第30课课文。整句如下：

Since the sea covers the greater part of the earth's surface, it is quite reasonable to regard the sea floor as the basic form of the crust of the earth, with, superimposed upon it, the continents, together with the islands and other features of the oceans.

划线部分为with复合结构作补充性说明，即with后接复合宾语。红色部分为过去分词短语作宾补。由于with的宾语continents被together with...介词短语后置修饰，导致宾语很长，所以宾补前移插入到with和continents之间，用逗号隔开，提示这是with复合结构的宾补。试比较：

with the continents, together with the islands and other features of the oceans， superimposed upon it.