B. B. Warfield, so far as I know, did not have any direct conversation or exchange of letters with Charles Darwin. Other people did engage the scientist on his views of God and Scripture. One of those was Asa Gray, the botanist. He exchanged letters trying to get Darwin to be open to the idea of God working in the world. In the end Darwin died, by his own words, as an agnostic.
Warfield engaged in a dialogue with the written works of Darwin. By Dialogue I mean an informed interchange of ideas. A dialogue is not a screaming fit, nor is it a congratulatory slap on the back. It is a frank discussion.
When Paul was in Athens, as recorded in Acts 17, he engaged in dialogue. He did not always preach, sometimes he got into the places where people meet and talk, and dialogued.
16 Now while Paul was waiting for them at Athens, his spirit was provoked within him as he saw that the city was full of idols. 17 So he reasoned in the synagogue with the Jews and the devout persons, and in the marketplace every day with those who happened to be there.
Can you see him, there in the market place and on the covered porticos of Athens talking with those who gathered to talk. Presenting his view to challenge and engage their views. This was a normal thing in Athens. For as we saw:
21 Now all the Athenians and the foreigners who lived there would spend their time in nothing except telling or hearing something new.
The 19th century version of this was to write in scientific or theological periodicals. The Old Princetonians lived in a time where a scholar in one field could keep up with the general outlines of human knowledge by reading such articles. They could keep up with the fields of geology and biology. And as Darwin had made such a big splash in the world, they were able to keep up with the thinking of scientists at that time. They especially wanted to engage in those places where science and faith meet.
Another passage comes from the book of I Peter 3:13-17
13 Who is going to harm you if you are eager to do good? 14 But even if you should suffer for what is right, you are blessed. “Do not fear their threats; do not be frightened.” 15 But in your hearts revere Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect…
Full Sermon – Dialogue (corrected version)