Translations for trail in French

Here are paragraphs from public domain books translated:
"I think that this should do," said he, glancing into the glass above the fireplace. "I only wish that you could come with me, Watson, but I fear that it won't do. I may be on the trail in this matter, or I may be following a will-of-the-wisp, but I shall soon know which it is. I hope that I may be back m a few hours." He cut a slice of beef from the joint upon the sideboard, sandwiched it between two rounds of bread, and, thrusting this rude meal into his pocket, he started off upon his expedition. — Je crois que cela ira, dit-il en jetant un coup d’œil sur la glace au-dessus de la cheminée. Je voudrais que vous puissiez venir avec moi, Watson, mais je crains que ce ne soit nuisible. Suis-je sur la vraie piste ou n’est-ce qu’un leurre ? en tous cas je le saurai bientôt. J’espère revenir sous peu. Il alla au buffet, se coupa une tranche de bœuf, qu’il plaça en sandwich entre deux morceaux de pain, et mettant ce repas sommaire dans sa poche, il partit en expédition.
The Adventures of Sherlock Holmes, by Arthur Conan Doyle Les Aventures de Sherlock Holmes, de Arthur Conan Doyle
"Look at this!" said he. "By George, this must be the trail of the father of all birds!" — Regardez ! dit-il. By George ! voici, j’imagine, les traces de l’ancêtre des oiseaux.
The Lost World, by Arthur Conan Doyle Le Monde perdu, de Arthur Conan Doyle