In the instant case, the instrument does not expressly identify the particular indebtedness to be assumed. Nonetheless, parol evidence is admissible for the purpose of making the identification. National Bank of Commerce of Houston, Tex. v. Irvine, 73 S.W.2d 929, 931 (Tex.Civ.App. — San Antonio 1934, writ ref'd); Schumacher Oil Works v. Keisler, 31 S.W.2d 461, 463 (Tex.Civ.App.-Galveston 1930, no writ). The extrinsic evidence received by the court does not vary or contravene the language of the divorce decree but rather clarifies and explains the essential agreement contemplated by the parties.

And manifestly, whether the indebtedness is suit was the obligation referred to in the letter from this debtor seeking further time and promising payment, was a question of fact either for the court or jury. Schumacher Oil Works v. Keisler, Tex.Civ.App., 31 S.W.2d 461. Moreover, it was defendant's burden to show that his acknowledgment is not referable to the indebtedness in suit.

An agreement of assumption need not expressly identify the particular debt to be assumed. 28 Tex.Jur. p. 264, § 167; Schumacher Oil Works v. Keisler (Tex.Civ.App.) 31 S.W.2d 461. And parol evidence is admissible for the purpose of that identification.