1. He cried out to them from across the room.

across在这里是介词，不是副词。from可以后接介词短语，例如：from behind the door, from under the bed. 等于from somewhere/a place behind the door, from somewhere/a place under the bed。from across the room = from a place across the room.

他从房间另一边朝他们喊话。

from 介词短语表示声音的发源地，to介词短语表示声音的目的地，out表示方向，三者均为状语。

2 The idea of being in contact with all those silhouetted shadows he saw thronging before the windows and passing in and out of the doors across the street — it gave him a nausea.

破折号之前是一个名词词组，中心词为the idea。of being...shaddows为介词短语作定语修饰diea, 表示同位关系。he saw thronging...and passing...street，为省略了作宾语的关系代词的限制性定语从句，修饰shaddows。二个分词短语thronging和passing为定语从句中感官动词saw的宾语补足语。破折号可以用逗号替换（比逗号更为强调）。it 指代以idea为中心词的整个词组。这个词组语法上叫做左偏置结构。与下面句子结构相同：

Your daughter，she is beautiful.