NATURES HEIBOOLYPHICS. 149 



Occurrence and Means of Preservation. 



Fossil footprints have been found in various parts of the world, as 

 in England, German}-, France, and, in our own country, in the Grand 

 Canon of the Colorado, as well as in association with Jurassic dinosaurs 

 in the northwest ; but it is in the valley of the Connecticut and in rocks 

 of the same formation in New Jersey that they occur in an abundance 

 and perfection of preservation which is unrivaled elsewhere. 



In this region sandstone beds of great thickness occur which every 

 now and then exhibit impressions with generally something of an in- 

 terval between the track-bearing layers. 



Geologists have been led to suppose that the broad valley of the 

 Connecticut was during Triassic times a tidal estuary extending from 

 the village of Northfield, Mass., to New Haven, a distance of one hun- 

 dred and ten miles, with an average width of twenty miles. In places 

 in this estuary were mud flats, some well out in the ancient bay, others 

 nearer the shore, which were left bare by the receding tides. Here the 

 animals loved to congregate, possibly they came for food, but it seems 

 more likely that the dinosaurs here assembled at certain seasons for 

 mating as the seals do in the Alaskan rookeries. 



The means of preservation were threefold, of which the first was 

 the fierce heat of a tropical sun, for plant remains indicate that such 

 climatic conditions prevailed, while the second and third are really 

 attributable to one cause, volcanic activity. This resulted in the 

 formation of the Holyoke and Mt. Tom ranges and in broad lava flows. 

 Upon these sheets the sand and silt were deposited, forming thus the 

 tidal flats where the creatures congregated. The heat of the cooling 

 lava added its baking effect to that of the sun, while the decomposing 

 lava liberated an iron cement which completed the task of solidifying 

 the overlying material into rock. 



The impressions made when the tide had ebbed were thus somewhat 

 hardened before the incoming flood bearing its burden of sediment 

 gently buried the traces without the least injury, thus preserving for 

 our enlightenment these monuments of the past. 



