NO. 23.] CENTRAL CONNECTICUT IN THE GEOLOGIC PAST. 13 



four is longer than the sum of all succeeding eras, but as to the 

 duration of the first two eras not even their ratio to the later 

 times is known. In the region selected for the present study the 

 history can be well deciphered as far back as the beginning of the 

 Mesozoic era, and it will be seen that many events which have 

 transformed the face of nature have been crowded into that time. 

 Yet it is probably not more than the last fourth of that geologic 

 time which has elapsed since the beginning, in the Cambrian, 

 of the fossil record of living forms ; nor more than a tenth of the 

 entire history of the world. The length of the geologic periods 

 is measured by the work of erosion and deposition; and the 

 changes which have passed over central Connecticut from period 

 to period, as expressed in the accompanying drawings, enable the 

 reader to form some estimate for himself of their relative dura- 

 tion. In most cases it is seen that each preceding change involves 

 a greater transformation and implies a longer lapse of time than 

 those which follow, corresponding thus to the estimates of the 

 table. But knowledge becomes vague in proportion as the 

 evidence has been obliterated in the recording of later events, 

 and the student of geologic time looking over the illimitable 

 past sees the vista recede like a mountainous landscape. Beyond 

 the near-by foothills range after range breaks the view, each 

 rising higher, the scale of magnitude continually increasing; 

 but the eye gradually loses all detail of form. Beyond the blue 

 horizon's rim the reason knows still other mountains lie. 



