ゆく used in auxiliary sense - instead of いく?


I'm reading a novel 「キッチン」by 吉本ばなな at the moment and I noticed that she uses
ゆく in some places as an auxiliary verb to signify the action progression from
here or from now (if my understanding is correct). I can quote two examples:

> 雨に覆われた夜景が闇ににじんで **ゆく** 大きなガラス、に映る自分と目が合う。
>
> [...] はるかに淡い空に薄い雲がゆっくりと流れて **ゆく** 。

So far in my study of Japanese I have encountered いく used this way. Can ゆく be
used the same way? Will those sentences have the same meaning if ゆく was
replaced by いく? Is ゆく commonly used this way in modern Japanese?




I agree with `l'électeur` that it is quite common to pronounce `言{い}う` as
`言{ゆ}う` for example...

> そんなこと言{ゆ}った気{き}がしたな～

However going back to ゆく

`行{い}く` although often interchangeably pronounced `行{ゆ}く` when spoken, is also
written that way commonly when referring to things like destination

> 東京{とうきょう}行{ゆ}き電車{でんしゃ}まもなく発車{はっしゃ}いたします

In more detail (and taken from a Japanese Q and A site)
<http://oshiete.goo.ne.jp/qa/1637122.html> - 日本語

> > 『ゆく』は、時の経過を表し、『いく』は、人、物の移動を表す、と思いますが。
>
> The `ゆく` reading represents the passage of time, wheras `いく` is used when
> referring to a person, representing the movement of goods.

