CLlIsrATE OF HISTORIC TIMF.S 551 



note that of the nineteen great floods on record eighteen occurred in the cold 

 season between the autumnal and vernal equinoxes. 



"The second remarkable phenomenon mentioned by the chronicles is the 

 freezing of the entire Baltic, which occurred many times during the cold win- 

 ters of these centuries. On such, occasions it was possible to travel with car- 

 riages over the ice from Sweden to Bornholm and from Denmark to the German 

 coast (Lubeck), and in some cases even from Gotland to the coast of Estland." 



These quotations are particularly significant when compared with the 

 conclusions drawn from the growth of trees in Germany and the distribu- 

 tion of storms as given by Kullmer. A careful reading of Pettersson's 

 statements shows that we have to deal with two distinct types of phe- 

 nomena. In the first place, the climate of central Europe seems to have 

 been peculiarly continental during the fourteenth century. The winters 

 were so cold that the rivers froze, and the summers were so wet that 

 there were floods every other year or oftener. This seems to be merely 

 an intensification of the conditions which we have already seen to prevail 

 at the present time during periods of many sun-spots, as indicated by the 

 growth of the Eberswalde trees and by the number of storms in winter as 

 compared with summer. The prevalence of droughts, especially in the 

 spring, is also not inconsistent with the existence of floods at other sea- 

 sons, for one of the chief characteristics of a continental climate is that 

 the variations from one season to another are more marked than in 

 oceanic cliriiates. Even the summer droughts are typically continental, 

 for when continental conditions prevail, the difference between the same 

 season in different years is extreme, as is well illustrated in Kansas. 



The second type of phenomena described by Pettersson is, as he takes 

 pains to state, peculiarly oceanic in character. It consists of two parts, 

 both of which are precisely what would be expected if a highly conti- 

 nental climate prevailed over the land. In the first place, at certain times 

 the cold area of high pressure, which is the predominating characteristic 

 of a continent during the winter, apparently spread out over the neigh- 

 boring oceans. Under such conditions an inland sea, such as the Baltic, 

 would be frozen, so that carriages could cross the ice even in the far west. 

 In the second place, because of the unusually high pressure over the con- 

 tinent, the barometric gradients apparently became intensified. Hence 

 at the margin of the continental high-pressure area the winds were un- 

 usually strong and the storms of corresponding severity. Some of these 

 storms may have passed entirely, along oceanic tracks, while others in- 

 vaded the borders of the land, and gave rise to the floods and to the 

 wearing away of the coast described by Pettersson. 



Another highly significant fact in this connection appears in the curve 



