请各位老师看一下这两个句子是哪种结构，是不是是定语从句？关系词后面引导的为何是个短语?以下两句摘自剑桥雅思。
1. Like many other substances regarding the origin of which there existed some obscurity and mystery , ambergris in former time possessed a value, and had properties attributed to it, more on account of the source from which it was drawn than from its inherent qualities .
这里的of which 是定语从句吗？若是which 指代什么？存在mystery of origin这种关系吗？
2. As Drucker saw it, the age of mercantilism in which economics was the only force that to need to be considered was dead.
这里的that的先行词是force吗？为何that后面不是一个句子？
请各位老师剖析指教。谢谢！
1 regarding the origin of which there existed some obscurity and mystery 这是定语从句，which指代先行词substances。regarding the origin of which = regarding the origin of the substances, 为目前分词短语在定语从句中作方面状语
2 这个句子中that应该引导定语从句修饰the only force, 但that后接to need肯定是错误，可能是传抄或输入错误把。to need应改为needed。
