We looked out across a river valley to the broad snow-white ridge of mount Ararat， its peak incandescent against the blue sky.

【原翻译】我们远望，越过河谷看见了广阔的雪白的亚拉腊山山脊，它的顶峰在蓝天的映衬下闪闪发光。

原翻译不错。把 to 翻译成“看见”，把against 翻译成“映衬”，确实好。

不过，作为文学语言，原翻译仍嫌不足，我感到还有改进的地方，因为out 没有译出。我重新翻译如下：

【翻译】我们朝外远眺，越过河谷看见了阿勒山那广阔的白雪皑皑的山脊，山顶在蓝天的映衬下熠熠发光。

注：红色部分为修改后的。

its peak incandescent（adj. 发光的） against the blue sky. 是独立主格结构，其构成为：

逻辑主语 + 形容词短语。

如果加was，说明它是一个完整的句子，需要用连词连接，或者单独成句。例如：

1. We looked out across a river valley to the broad snow-white ridge of mount Ararat， and its peak was incandescent against the blue sky.

2. We looked out across a river valley to the broad snow-white ridge of mount Ararat. Its peak was incandescent against the blue sky.

以上两句比较呆板，语法虽然不错，但缺少文学语言的韵味。

我举两个类似的例子：

Her face pale with anger, she rose to go away. 　

I saw a deep pond, the water blue like the sky.