MARTHA, St, or Sierra Nevada, a very high mountain in New Spain. Some say it is 100 miles in circumference at the bottom, and five miles in height. The top is always covered with snow in the hottest weather; and the French affirm, that they can perceive it from the island of St Domingo, which is 370 miles distant. W. Long. 74. 35. N. Lat. 8. 0.