1. But while the earth has slumbered,all the air has been alive with feathery flakes descending,as if some northern Ceres reigned,showering her silvery grain over all the fields.

解析:本句的主干为:all the air has been alive。While引导让步状语从句，意为“尽管大地还在酣睡”；介词短语with feathery flakes descending作状语，表示伴随。As if意为“好像”，引导方式状语从句；现在分词短语showering..作状语，表伴随。

2. The snow lies warm as cotton or down upon the window-sill;the broadened sash and frosted panes admit a dim and private light,which enhances the snug cheer within.

解析:本句包含两个简单句,由分号隔开。分号前为第一个分句，其主干为The snow lies warm…or(lies)down upon the window-sill。第二个分句的主干为the…sash and…panes admit a…light,which至句末为定语从句修饰light，说明这光线的作用。