272 



University of California Publications. 



[Geology 



for the entire west coast give a mass of detail which can be 

 studied best by expressing the figures for a limited period by 

 isothermal lines. In PL 32 is given the general result for the 

 month of August. 



A salient feature of this chart is the area indicating warmer 

 water to the north of the inshore belt of cold water as well as 

 to the west and south. The fact of the presence of this warmer 

 water in addition to the minor belts of varying temperature 

 already shown in PL 31 seems to exclude entirely the hypothesis 

 of a cold, polar surface current along the west coast of North 

 America. The only remaining explanation is that there exists 

 a belt of cold water upwelling from the adjacent ocean depths. 

 Possible reasons for this upwelling will be discussed later. A 

 prior consideration is the general trustworthiness and the de- 

 gree of accuracy of the isotherm in PL 32. The writer feels con- 

 fident that the location of the coldest part of the inshore belt in 

 the vicinity of Cape Blanco and Cape Mendocino and the exist- 

 ence of warmer water to the northward are fully established. 

 The exact position of the isotherms is open to doubt but it is not 

 believed that the error is sufficient to affect the general relations 

 which can be shown on a map of the scale used in PL 32. More- 

 over the problems and conclusions of the paper will not be 

 changed by a future shifting of the boundaries of the tempera- 

 ture zones here represented. 



The essential differences between the chart here presented 

 and previous isothermal charts of the North Pacific for the 

 month of August will now be examined. The charts to be cited 

 show little if any variation in the location of the isotherms in 

 mid-ocean, but differ widely in the vicinity of the American 

 Coast. Marakoff in his work already quoted makes the isotherm 

 of 18° C. turn abruptly to the southward at about latitude 45° 

 and again bend to meet the coast in about latitude 36°. He thus 

 represents the cold belt along the coast as merely an extension 

 of the cold zone of the extreme North Pacific. The British 

 Admiralty charts (1886) show the isotherm of 60 & as almost 

 touching the coast near the mouth of the Columbia River and 

 then as swinging out and southward, finally meeting the coast 



