88 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
the south side of the Rio Soto la Marina. This, then, must be taken as 
the dividing line, or parallel of transition , of the Tamaulipan fauna and 
flora, separating the more Tropical from the more Temperate region. I 
here acknowledge with pleasure my indebtedness to Mr. Thomas B. Bar¬ 
bour, Inspector of the Bureau of A. I., at Brownsville, for the informa¬ 
tion on the country in the vicinity of the Soto la Marina river. 
Oaxaca and its vicinity are not Tropical. The city lies in a valley 
about 5000 feet above the level of the sea. It is, with all the country 
round it, distinctly Lower Sonoran. The country between Oaxaca and 
Puebla, along the line of the railway, must be considered entirely Lowe'r 
Sonoran. At one place only does it approach the Tropical , where the 
Grande and Solado rivers join their waters to form the Rio Quiotepec, 
which in its lower course is known as the Rio Papaloapam. This point 
is less than 2000 feet above the sea. In other places along the railway, 
the tall cacti, bare and rocky hill-sides, and dry air speak for themselves 
and betoken the Loicer Sonoran. 
On the west coast of Mexico, the Tropical extends much farther north 
than on the east. It is also confined to a very much narrower strip. The 
Loire)' Sonoran likewise extends much farther north on the west. The 
most potent reasons exist for this great difference in the east and west 
coast regions. The warm Pacific ocean currents are uniformly quoted as 
reasons for this much greater warmth on the west coast. But this is not 
all; another and opposite cause produces the other result on the east 
coast. The whole Atlantic slope bordering the west side of the Gulf of 
Mexico, extending up through Texas, Eastern New Mexico, Oklahoma, 
and Kansas, is liable during the whole year, except from June to Aug¬ 
ust, to strong and continued cold winds from the north, known to the in¬ 
habitants as “ northers.” The influence of these is felt on the Mexican 
coast far to the south of Vera Cruz. Speaking from my own experience, 
* “ northers” are not felt in Kingston, Jamaica. The reason is that the 
warm waters of the sea intervene to warm the winds before they reach 
that latitude. But on the Gulf of Mexico slope these winds sweep down 
from the far north, gaining strength across the great plains, but gaining 
little heat, and follow the Mexican coast southward until they become 
warmed and lost in the heated air of the tropics. On the Pacific coast no 
such conditions prevail; the ocean currents traveling northward oppose 
their warming influence to north winds, and the physical conformation 
of the country prevents the birth of “northers.” 
