A few hours in the dark, and we reach Orizaba.  We have changed our climate for the last time to-day, and have reached that district where tobacco flourishes at an altitude of 4,000 feet above the sea.  But of this we see nothing, for we are off again long before daylight; and by the time that external objects can be made out we find ourselves in a new region.  A valley floored with rich alluvial soil from the hills that rise steeply on both sides, their tops shrouded in clouds.  Signs of wonderful fertility in the fields of maize and barley along the roadside.  The air warm, but full of mist, which has already penetrated our clothes and made them feel damp and sticky.  “Splendid country, this, Senores,” said an old Mexican, when he had twisted himself round on his seat to get a good stare at us.  “It seems so,” said I, “judging by the look of the fields, but it is very unpleasantly damp just now.”  “Just now,” said the old gentleman, echoing my words, “it is always damp here.  You see that drizzling mist; that is the chipi-chipi.  Never heard of the chipi-chipi!  Why it is the riches and blessing of the country.  Sometimes we never see the sun here for weeks at a time, and it rains a little every day nearly; but look at the fields, we get three crops a year from them where you have but one on the fields just above.  And it is healthy, too; look at those fellows at work there.  When we get up to the Llanos you will see the difference.”

The valley grew narrower as we drove on; and at last, when it seemed to end in a great ravine, we began to climb the steep hill by a zig-zag road.  Soon the air grows clearer again, the sunshine appears and gets brighter and brighter, we have left the mist behind, and are among ranges of grand steep hills, covered with the peculiar vegetation of the plateau,—­Cactus, Opuntia, and the Agave Americana.  In the trough of the valley lies a regular opaque layer of white clouds, hiding the fields and cottages from our view.  We have already passed the zone of perpetual moisture, whose incessant clouds and showers are caused by the stratum of hot air—­charged with water evaporated from the gulf—­striking upon the mountains, and there depositing part of the aqueous vapour it contains.

You may see the same thing happening in almost every mountainous district; but seldom on so grand a scale as here, or with so little disturbance from other agents.  Yesterday was passed in the “tierra caliente,” the hot country; our journey of to-day and to-morrow is through the “tierra templada” and the “tierra fria,” the temperate and the cold country.  Here a change of a few hundred feet in altitude above the sea, brings with it a change of climate as great as many degrees of latitude will cause, and in one day’s travel it is possible to descend from the region of eternal snow to the utmost heat of the tropics.  Our ascent is more gradual; but, though we are three days on the road, we have sometimes scarcely time to notice the different zones of vegetation we pass through, before we change again.