228 GEOLOGY, 



Cambrian strata were not deposited there, or the Upper Cambrian 

 beds, once deposited, have since been removed by erosion. Between 

 these alternatives the figure does not decide. 



If section 3 be compared with section 4, it will be seen that the 

 latter lacks the Middle Cambrian as well as the Upper, the Lower 

 resting, as before, unconformably on the Proterozoic. This section 

 might mean either that the area where it occurs emerged from the 

 sea before the Middle Cambrian epoch, or that such Middle and Upper 

 Cambrian beds as were once deposited there have since been carried 

 away by erosion. 



From section 7 it is seen that the Lower Cambrian of eastern New 

 York has extraordinary thickness, compared with the areas farther 

 northeast. As in the case of sections 1 and 2, this may mean either 

 that the reign of section 7 was under water longer during the Early 

 Cambrian epoch, or that sedimentation was here more rapid. The 

 rapid rate of accumulation might be accounted for in more than one 

 way. If the area of section 7 was near a coast, and especially if the 

 adjoining land was high, rapid sedimentation would be likely to fol- 

 low. If at the same time the formations of the land were easily eroded, 

 the rate of sedimentation would be still further increased. Rivers 

 may have come into the sea in this vicinity with heavy loads of sedi- 

 ment, or shore currents may have been such as to allow of exceptionally 

 rapid accumulation of sediments at this point. 



The Upper and Middle Cambrian of section 8 are somewhat thinner 

 than the corresponding series in sections 1, 2, and 6. So far as the 

 Upper Cambrian is concerned, the thinness might be due to the re- 

 moval of its upper part by erosion; but the thinness of the Middle 

 Cambrian, taken together with its conformity above and below, seems 

 to indicate that the accumulation of sediment was here relatively slow 

 during this epoch. The study of the various sections may thus be 

 made to throw light upon the conditions which existed at the points 

 where sections are known. 



In the areas where sections 1 to 11 and 13 to 17 occur, the Lower 

 Cambrian strata are present. This means that the Lower Cambrian 

 seas covered these areas. On the other hand, sections 18 to 28 sug- 

 gest, by the absence of the Lower Cambrian formations, that the sea 

 did not occupy the areas where these sections occur in the Lower Cam- 

 brian epoch. The only alternative is that the Lower Cambrian rocks 



