麻烦各位牛人帮我分析一下这句话

heibantou

Particularly interesting are a series of collections which continue to document the evolution of ceremony and of material forms for which the department already possesses early (if not the earliest) collections formed after the frist contact with Europeans.

其中想问问，第二个WHICH是指前面哪个词？collections 还是 evolution,还有 for which 在这里是怎么个用法，代表什么意思，如果有牛人能给翻译一下，就更好了，谢谢各位

我心向明月

大哥，这句话从哪里弄出来的？