224 New York State Museum 



it again until Upper Cambrian time,. and there was a 

 long interval of erosion before the introduction of a 

 new cycle of deposition. 



Throughout Middle and Upper Cambrian times the 

 continent of North America was a lowland, permitting 

 the seas to encroach widely upon the lands. High- 

 lands, if any, were to be looked for only in the border- 

 lands of Cascadia and Appalachia. The Killarney 

 mountains in the center of the interior lowland were 

 reduced to a low upland. Since the greater part of 

 the Appalachian trough was not occupied by marine 

 waters, here the Upper Cambrian beds, where present, 

 rest as a rule upon Lower Cambrian (southern Appa- 

 lachian region). As we have seen, the seas of the 

 Lower Cambrian were restricted to the two great 

 troughs or geosynclines. During the Middle Cam- 

 brian the eastern trough was largely drained of Atlan- 

 tic waters, but once or twice during this epoch marine 

 waters teeming with life common to the western (Cor- 

 dilleran) trough spread eastward into it. In Upper 

 Cambrian times continental seas of wide extent, with 

 faunas mainly of western origin, were developed, espe- 

 cially in the Mississippi basin. However, the Upper 

 Cambrian faunas of the southern Appalachian region 

 are mainly of Atlantic origin and very different from 

 the western life of the same epoch. 



The Middle Cambrian beds in the east are particu- 

 larly well developed in the Acadian region of eastern 

 Canada and hence this series of beds is known as the 

 Acadian series. The marine waters then occupying 

 this region belonged to the Atlantic Province. The 

 deposits consist mainly of shales although there are 

 some thin limestone beds. There is very little sand 



