Thorp, James, and Leslie Rockwell Smith. “CONCERNING THE ORIGIN OF THE WHITE QUARTZ SANDS OF NORTHERN PUERTO RICO”. The Journal of Agriculture of the University of Puerto Rico 17, no. 2 (April 1, 1933): 157–170. Accessed April 27, 2024. https://revistas.upr.edu/index.php/jaupr/article/view/14248.