PHYSICAL AND CLIMATAL CONDITIONS. 137 



been a little lower in mean temperature, but less extreme 

 tlian that of North America at the present day. It is 

 farther to be observed that the Pleistocene marine fauna 

 is a little less boreal in New England than in the St. 

 Lawrence valley, and that further north in Hudson's 

 bay and the arctic coasts, it is not very dissimilar from 

 that of the St. Lawrence. 



In the later glacial period, that of the Saxicava sand, 

 the great size and wide dispersion of boulders indicates 

 much heavy field-ice, and, consequently, a low temperature 

 of the sea, while the existence of local glaciers on the 

 high lands not submerged, also indicates a low temperature. 

 To this corresponds the vast predominance of the species 

 Saxicava rugosa in the lower part of the Saxicava sand. 

 There would, in tliis period, seem to have been fluctuations 

 in temperature, due, perhaps to elevations and depressions 

 of land, so that while in some of the raised beaches the 

 indications of ice-drift are not so extreme as at present, 

 on other levels there are gigantic boulders, and some 

 of these carried far. Thus the later Pleistocene was 

 characterized at once by great variations in the elevation 

 of the land and by corresponding vicissitudes of climate. 



These few remarks will, I think, suffice on this subject, 

 when taken in connection with the facts and principles 

 stated beforehand in chapter first. 



An interesting illustration of the effects of varying 

 distribution of land and water, may be taken from that 

 warm period already alluded to as intervening between 

 the glacial and modern times, and coinciding with the 

 second continental period of Lyell, as evidenced by the 

 distribution of marine animals at present on the coasts 

 of Nova Scotia and New England. This peculiarity of 

 distribution attracted my attention, as a collector of 



