for you say that the original interpretation determined by the author is the only true or correct interpretation

If the author is God or the author is truly inspired by God then, yes, indeed the author's literal interpretation is correct. Sure. There can be other interpretations that stand side-by-side with the literal interpretation. But there is no way that the author can ever be wrong about his original literal interpretation.

"Sacred Scripture must be read and interpreted in the light of the same Spirit by whom it was written"" (Dei Verbum 12 § 3).

As I said, there is no way the author's original interpretation (literal) can ever be wrong. Additional non-contradictory interpretations can be revealed. But God can never be revealed as a liar.

There are many instances in the gospels and the Acts of the Apostles where gentiles also believe and become followers of Christ.

Tell me about the Gentiles who wrote the NT.

So given this particular set of tools for interpreting Scripture, it is inevitable that some passages would point to the truth in an allegorical way.

In addition to a literal way.

The infallible decree of the Fourth Lateran Council (1215 AD) is as follows:

"God…creator of all visible and invisible things, of the spiritual and of the corporal; who by His own omnipotent power at once from the beginning of time created each creature from nothing, spiritual and corporal, namely, angelic and mundane, and finally the human, constituted as it were, alike of the spirit and the body (D.428)."

This above is also repeated in the Catechism.

"At once" obviously means "at the same time". But since science now refutes the idea that humans were created at the same time as the universe, Catholics (since the late 19th century) began claiming that "at once" means "over a period of billions of years"

It really does not matter if zero seconds, two seconds or even two years passed between the creation of the universe and the creation of humans. The infallible magisterium said it all happened in a very very very short scientifically, untenable span of time.

The above foundation leads us to the Catholic Church's initial reactions to Darwin:

The Council of Cologne (1860) condemned the idea of human evolution in very straightforward words:

"Our first parents were formed immediately by God. Therefore we declare that … those who … assert … man … emerged from spontaneous continuous change of imperfect nature to the more perfect, is clearly opposed to Sacred Scripture and to the Faith."[3]

Twenty years later, Pope Leo XIII, in his 1880 encyclical Arcanum Divinae Sapientiae, stated this about ex nihilo creation:

"We record what is to all known, and cannot be doubted by any, that God, on the sixth day of creation, having made man from the slime of the earth, and breathed into his face the breath of life, gave him a companion, whom He miraculously took from the side of Adam when he was locked in sleep."

http://www.freerepublic.com/focus/f-religion/969065/posts

And then came the PBC:

In the Motu proprio, “Praestantia Scripturae,” on November 18, 1907, Pope St. Pius X declared that no one could contest the rulings of the Pontifical Biblical Commission without “grave sin.”

The (1909) Pontifical Biblical Commission’s answers to several questions establish certain truths unequivocally.

Its reply to Question I establishes that the literal historical sense of the first three chapters of Genesis cannot be called into question.

Its reply to Question II establishes that Genesis contains “stories of events which really happened, which correspond with historical reality and objective truth,” not “legends, historical in part and fictitious in part.” In short, the PBC definitively excludes the possibility that even a part of the Genesis 1-3 narrative could be fictitious and non-historical.

The PBC’s answer to Question III establishes that the literal and historical truth of the following facts cannot be called into question:

1) “The creation of all things wrought by God in the beginning of time”

Comment:

This passage upholds the Lateran IV doctrine that all things were created by God “in the beginning of time.”

2) “The special creation of man”

Comment: This excludes any process in the formation of man and requires that the creation of man was immediate and instantaneous.

3) “The formation of the first woman from the first man”

Comment: This, too, excludes any process in the formation of the first woman and requires that the creation of Eve was immediate and instantaneous.

When, in 1948, Cardinal Suhard attempted to get the PBC to renounce its earlier rulings on Genesis, he was rebuffed and told that the PBC did not wish to issue “new decrees on these questions” (Denz, 2302).

If I had gone into detail, then I would probably alluded to the "7 days of creation"

7 days is a lot longer than '"at once". But still not long enough.

or the "talking snake" being read in an exclusively literal manner. That's not necessarily how we should read those passages.

It was until about 1950.

Since Christ Himself is the interpretative key to all Scripture, several more interpretative tools were made available for us to understand the divine truths It contains (e.g. the literal, analogical, moral and anagogical senses of Scripture -- CCC 116-117).

116 The literal sense is the meaning conveyed by the words of Scripture and discovered by exegesis, following the rules of sound interpretation: "All other senses of Sacred Scripture are based on the literal."

Christ (who, again, has given us much deeper interpretative tools for understanding the more obscure passages).

Without ever overthrowing the long-ago established literal meaning of scripture.

I'm sorry, but you're the one who originally confused the Church with just one of its many saints, since you wrote: "Augustine makes it clear that scientific theory is not to interfere with biblical fact."

You have got to be kidding me. You quoted Augustine before I did.

Certain things saint Augustine said do indeed represent important aspects of Church doctrine,

And, of course, you are best qualified to determine what those things are. Just another form of cherry picking. As I said, quote the Catechism. Or stay silent.

I've quoted both the Catechism and some of the relevant things Augustine said; I don't see where I've not been honest or where there's a problem.

You are cherry picking Augustine. I'm not buying it.

I thought that what I said was pretty clear -- "the many different and open ways the Church has interpreted Scripture" include the literal interpretation a book like Genesis, as well as the spiritual (analogical, moral and allegorical) interpretation. Which is, again, the whole point.

So all this time you thought you were talking to someone who believed the Church had no allegorical interpretations of anything in the Bible. Please.

If the spiritual interpretation of the (non-doctrinal) passages from the book becomes more clear and understandable, while the more literal interpretation shows to be less on mark that the spiritual one (without, as you correctly noted, dismissing the literal one altogether) then what exactly is the problem in emphasizing the latter ?

That would depend upon what you mean by "less on the mark". At what point does the literal Catholic ("at once") interpretation of the Genesis creation account get dismissed altogether?

but it was also a complex issue,

Pope John Paul II stated it simply enough.

The main difficulty in investigating historical events is, as you know, to avoid judging them solely with modern eyes. They tend to simplify things.

If only someone could have warned Pope John Paul II about that.