Reading the following Scriptures will demonstrate that this  gift of tongues is not the same as the unknown tongue.

1 Corinthians 14:21-22 In the law it is written, With [men of] other tongues and other lips will I speak to this people; and yet for all that will they not hear me, saith the Lord.  Wherefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying [serveth] not for them that believe not, but for them which believe.   
   
1 Corinthians 14:26-28 How is it then, brethren? when ye come together, every one of you hath a psalm, hath a doctrine, hath a tongue, hath a revelation, hath an interpretation. Let all things be done to edifying.   If any man speak in an [unknown] tongue, [let it be] by two, or at the most [by] three, and [that] by course; and let one interpret.   But if there be no interpreter, let him keep silence in the church; and let him speak to himself, and to God. 

1 Corinthians 14:39-40 Wherefore, brethren, covet to prophesy, and forbid not to speak with tongues.  Let all things be done decently and in order. 

1Co 12:10 and to another workings of miracles; and to another prophecy; and to another discernings of spirits; to another divers kinds of tongues; and to another the interpretation of tongues:

2 Corinthians 3:6 Who also hath made us able ministers of the new testament; not of the letter, but of the spirit: for the letter killeth, but the spirit giveth life.