26 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



away, and erosion began weakly to etch once more into the low 

 floor of older rocks which was again exposed. 



At last, during the later Tertiary period, a movement of more 

 pronounced emergence began; the sea retreated, perhaps with 

 geologic rapidity, to the line of the present shore or even farther. 

 The rivers extended their lower courses across the low-lying and 

 newly exposed mantle of coastal plain sediments, flowing down 

 the gentle slopes in direct lines toward the sea. The unconsoli- 

 dated sands and clays were soon removed, but their presence had 

 served to permit the establishment of valleys diagonal to the older 

 structure. The rivers flowed in superimposed courses not in 

 harmony with the belts of softer rocks. Those of sufficient 

 erosive power, like the Connecticut below Middletown, have 

 maintained to the present their initial courses, cutting gorges 

 across the hard rocks which lay across their beds. Smaller rivers, 

 however, possess less erosive power, and have been deflected into 

 new channels following the outcrops of the less resistant rocks. 

 Upwarping and progressive tilting in several stages have con- 

 tinued, till now the old base-level of Cretaceous times passes above 

 that terraced and dissected surface of ancient rocks which con- 

 stitutes the Eastern and Western Highlands. 



According to this outline of Jurassic and Cretaceous history, 

 the structure section shown in Figure 5 applies to the time when 

 the shore was in the vicinity of central Connecticut. It shows 

 the time when the earlier generation of Appalachians had been 

 wholly effaced from Connecticut, and the present generation of 

 ridges and plateau remnants had not yet been born. Erosion had 

 completely severed the continuity of the landscapes of the 

 Cenozoic with the landscapes of the Mesozoic. 



But the hills carved from that uplifted peneplain still rise bold 

 and high in the Age of Man. They show that the time which has 

 elapsed since they were uplifted is far shorter than the time which 

 was required for the destruction of the previous order of 

 mountains. They give by contrast a vista of the vast duration of 

 the periods of the more remote past. 



The Block Mountains of the Early Jurassic, Figure 6. The 

 Triassic sediments of the Connecticut Valley and other areas in 

 eastern North America show by their fossils that they were 

 deposited in late Triassic time. Their deposition was closed by a 



