The general appearance of Graham's Island is represented in Fig. 22. Graham's Island was formed by accumulations of loose scoria and cinders, together with blocks of lava and fragments of limestone. It reached a height of 200 feet above the water, but only remained above the surface for a few months, when it was washed away, leaving a submarine bank some twelve miles in width, that was covered by water of about 150 feet, but which, however, increased rapidly in depth towards the edge until depths of from 1,200 to 2,000 feet were reached. [Illustration: FIG. 22. GRAHAM'S ISLAND--A RECENT VOLCANIC ISLAND] According to Lyell, on the 28th of June, 1831, before Graham's Island appeared, a ship passing over this portion of the sea felt severe earthquake shocks. On July 10th of the same year, the captain of a vessel from Sicily reported that as he passed near this part of the Mediterranean, a column of water, 800 yards in circumference, was seen to rise from the sea to a height of sixty feet, and that afterwards a column of steam rising to a height of 1,800 feet was seen in the same place. On again passing the same region on July 18th, this captain found a small island about twelve feet in height, with a crater in its centre, that was throwing out volcanic materials, together with immense masses of vapor. The island thus formed grew rapidly, both in size and height. When visited at the end of July, it had attained a height of from fifty to ninety feet, and was three-quarters of a mile in circumference. By August 4th, it had reached a height of 200 feet, and was then some three miles in circumference. From this time, however, the island began to decrease in size, as the waves began to wash it away. By August 25th, it was only two miles in circumference. On September 3d, it had decreased to three-fifths of a mile in circumference, and continued to decrease until it entirely disappeared, so that in the year 1832, there were, according to measurements, some 150 feet of water over its former site. The Mediterranean Sea between Sicily and Greece is also especially liable to submarine activity. New islands appear and disappear so frequently that in this region they are almost regarded as common phenomena. There are many other parts of the ocean where submarine volcanic eruptions are common. This is especially the case in the narrowest part of the Atlantic Ocean between Africa and South America. Here there is a region situated partly above the equator, though for the greater part south of the equator, frequently visited by submarine eruptions, that are accompanied by earthquakes, by the agitation of the water, by the appearance of floating masses of ashes and scoriæ, as well as by columns of steam or smoke. Floating masses of ashes and scoriæ sometimes occur so thick as to retard the progress of vessels.