472 Sayles — Dilemma of Paleoclimatolo gists. 



that seasons existed in the Ordovician in latitude 35° 

 north. It would seem necessary to invoke some cool- 

 ing agent if the glaciers went some distance into 

 the sea, as they evidently did. Blackwelder 24 and 

 Kirk 23 both believe that there were seasons in Alaska 

 during these times. During the Beekmantown time great 

 vulcanism, mostly of the explosive kind, was going on in 

 the British Isles. Twelve thousand feet of volcanics, 

 mostly of an explosive nature, were deposited in the Lake 

 District alone. Vulcanism was also going on in other 

 parts of the world. In the case of the Niagara tillite of 

 Kirk, volcanic activity went on contemporaneously in 

 what is now the Penobscot Bay region of Maine. Kirk 

 speaks of vast thicknesses of volcanic materials in this 

 Paleozoic section of southeastern Alaska. In the case of 

 the Beekmantown, splendid banding with seasonal charac- 

 ters occurs in the section. Whether or not a great land 

 emergence is causally connected with wide-spread glacial 

 conditions is still an open question. 



In this paper the writer does not advocate Humphrey's 

 volcanic theory to the exclusion of any solar theory, or 

 any other theory that will explain interglacial episodes, 

 but to say with Schuchert that Humphrey's theory will 

 not answer, because periods of glaciation or cooling are 

 not found to accompany every period of vulcanism, is not 

 enough to disprove it. The criteria for the determination 

 of cool periods has increased in the last few years and 

 many formations must be examined again. Periodic 

 changes in our present climate due, according to Bruckner 

 and Huntington, to changes in solar heat, have been 

 observed, and the solar theories must be weighed care- 

 fully. If Manson's theory, or some modification of it, 

 can explain interglacial episodes satisfactorily, Manson 

 may be nearer the truth for parts of earth history than 

 has been supposed. 



This paper has been written in a spirit of inquiry rather 

 than of affirmation. The theory of seasonal banding is 

 on trial and as an advocate of that theory the writer 

 would ask geologists to suspend judgment until the evi- 

 dence for periods other than the Pleistocene and Permo- 

 Carboniferous has been presented. 



