Next morning I awoke with a dreadful headache and pain in my back, brought on either by the fatigue of the day before, or by having been tempted to eat some half-ripe guayavas when coming across the plains tired and hungry. I lay in the hammock until ten o'clock, and then feeling a little better, got on my mule and started. I was so ill as to be obliged to hold on to the pommel of my saddle and several times to get off and lie down. We had brought some "tiste" with us made from chocolate and maize, and drinks of this relieved me. I at last reached Libertad at four o'clock, and went to bed immediately. Having fasted all day in place of taking medicine, I rose pretty well next morning, and we rode through the forest to the mines, reaching them at noon on the 29th July, after an absence of nineteen days. CHAPTER 18. Division of Nicaragua into three zones. Journey from Juigalpa to lake of Nicaragua. Voyage on lake. Fresh-water shells and insects. Similarity of fresh-water productions all over the world. Distribution of European land and fresh-water shells. Discussion of the reasons why fresh-water productions have varied less than those of the land and of the sea. I SHALL ask my readers to accompany me on one more journey. I have described the great Atlantic forest that clothes the whole of the eastern side of Nicaragua. I have gone through the central provinces, Chontales, Matagalpa, and Segovia; from the San Juan river, the south-eastern boundary of Nicaragua, away to the confines of Honduras on the north-west. I now propose to leave the central provinces, amongst which we have so long lingered, and to describe one of my journeys to those lying between the great lakes and the Pacific. Whilst the country to the north-east of the lakes is mostly composed of rocks, of great age, geologically, such as schists, quartzites, and old dolerytic rocks, with newer but still ancient trachytes, that to the south-west of them is formed principally of recent volcanic tufas and lavas, the irruption of which has not yet ceased. Most of the land, resulting from the decomposition of the tufas, is of extreme fertility; and, therefore, we find on the Pacific side of Nicaragua, indigo, coffee, sugar, cacao, and tobacco growing with the greatest luxuriance. Nicaragua is thus divided into three longitudinal zones. The most easterly is covered by a great unbroken forest; the principal products being india-rubber and mahogany. The central zone is composed of grassed savannahs, on which are bred cattle, mules, and horses. It is essentially a pasturage country, though much maize and a little sugar and indigo are grown in some parts. The western zone skirts the Pacific, and is a country of fertile soil, where all the cultivated plants and fruits of the tropics thrive abundantly; the rich, fat land might, indeed, with a little labour, be turned into a Garden of Eden.