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CHAPTER XXIX. 



BRITISH CLIMATES AND THEIR CAUSES RAINFALL IN 



DIFFERENT AREAS AREAS OF RIVER DRAINAGE. 



BEFORE discussing the subject of rivers and river- 

 gravels and alluvia, I now come to other phenomena 

 connected with the physical structure of our island 

 and its geography generally ; and first, with regard to 

 the rain that falls upon its surface. If we examine the 

 best hydrographic maps of the Atlantic, we find on them 

 numerous lines and arrows showing the direction of the 

 flow of the ocea.n currents as first drawn by Captain 

 Maury. One great current flows from the Gulf of 

 Mexico, where the water in that land-locked area with- 

 in the tropics is exceedingly heated ; and flowing out of 

 the gulf, it passes E. and NE. across the ocean, and 

 so reaches the European area of the North Atlantic. 

 So marked is the heat of this immense current that, in 

 crossing from England to America, the temperature of 

 the water suddenly falls some degrees. Twenty years 

 ago, in crossing the Atlantic, I was in the habit early 

 in the morning of taking the temperature of the water 

 with one of the officers of the steamboat. We then 

 found that at about five o'clock in the morning for 

 several days, the temperature of the sea was always 

 about four degrees above the temperature of the air, 

 but quite suddenly, in passing out of the Gulf Stream, 

 at the same hour of the morning, the temperature of 



