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

1 Corinthians 14:2 For he that speaketh in an [unknown] tongue speaketh not unto men, but unto God: for no man understandeth [him]; howbeit in the spirit he speaketh mysteries. 

1 Corinthians 14:5-6 I would that ye all spake with tongues, but rather that ye prophesied: for greater [is] he that prophesieth than he that speaketh with tongues, except he interpret, that the church may receive edifying.  Now, brethren, if I come unto you speaking with tongues, what shall I profit you, except I shall speak to you either by revelation, or by knowledge, or by prophesying, or by doctrine? 

1 Corinthians 14:14-15 For if I pray in an [unknown] tongue, my spirit prayeth, but my understanding is unfruitful.  What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.

1 Corinthians 14:18-19 I thank my God, I speak with tongues more than ye all:  Yet in the church I had rather speak five words with my understanding, that [by my voice] I might teach others also, than ten thousand words in an [unknown] tongue.