NO. 23.] CENTRAL CONNECTICUT IN THE GEOLOGIC PAST. 9 



though its value may still be great in graphically explaining the 

 geologic history of the region. 



The surface of the earth, which alone is open to observation, 

 is, however, a changing surface, the product of erosion, separat- 

 ing that portion of the rocks which is invisible because destroyed, 

 from that other portion which is invisible because not yet brought 

 to the scene of destruction. From the study of this soil-clad 

 surface which intersects the original structure of the rocks, the 

 vanished portion above our heads may be as legitimately por- 

 trayed, by the same methods of reasoning and with the same 

 degree of accuracy, as the invisible structures below our feet. 

 The structure may then be progressively simplified by taking 

 away the effects of successive crustal movements and thereby 

 graphically show the structural evolution. 



The corresponding landscape may be restored for each stage 

 by invoking the principles which underlie erosion and deposi- 

 tion and applying these to interpret the relations between the 

 present and the past. It has been noted that the accuracy of 

 details in the structure section becomes less the farther they are 

 from the controlling surface of observation, and, in a similar 

 manner, the accuracy of the delineation of the ancient surface 

 of erosion becomes less the farther it is removed from relation- 

 ship with the present landscape. Limits are therefore reached in 

 geologic time as well as in hidden depth, beyond which inference 

 weakens and portrayal cannot go. 



The method has its value on the one hand in overcoming the 

 confusion of words and in visualizing impressively change follow- 

 ing change in the protean earth. It shows with some degree of 

 geologic precision the chronologic mile-posts of the flowing land- 

 scape. But the limitation of scale of the drawings precludes the 

 representation of details, such as met the eyes of. the changing 

 denizens of each age. The restoration of these bygone forms 

 of life and the scenes among which they lived requires the imagin- 

 ation and the pencil of the geologic artist. 1 



1 See Bulletin No. 24 of the Connecticut Geological and Natural History Sur- 

 vey, Triassic Life of the Connecticut Valley, by Richard Swann Lull, Professor 

 of Vertebrate Paleontology in Yale University. This bulletin treats in detail the 

 life of Triassic times as drawn in part from knowledge of the bones, but especially 

 from the wonderfully rich and unique footprint record of the Triassic rocks of 

 Connecticut arid Massachusetts. 



