& W. Ford— Embryonic Forms of Trilobites. 265 



given above, one in the valley and the other, a greater height, 

 upon its side, show, after making reasonable allowance for the 

 slope of the water, that the level of the highest flood was at 

 least 280 feet above mean sea-level. 



Daring the greatest flood, the Westfield River and the West- 

 field Little River, joining the waters from the Connecticut, 

 flowed south over the Poverty Plain into the Farmington 

 valley. The lower deposits in'this vicinity were made by the 

 Westfield Rivers before the overflow from the Connecticut 

 began. One of the first results of the overflow from the north 

 must have been to fill the former valley of the Westfield Rivers, 

 so that during the time of greatest flood the Hampton and 

 Poverty Plains must have been one continuous plain. 



The north end of the Poverty Plain is five feet higher 

 than the south end of the Hampton Plain, and while the latter 

 slopes twelve feet per mile the former slopes onlv three and a 

 third feet per mile. The material of the Poverty Plain is 

 finer than that of the Hampton Plain. The differences in 

 height, slope, and material, are all due to the confluence of the 

 three streams upon the Poverty Plain, and to the damming 

 of the water by the Southwick Divide. 



The Avenue Plain, at its western extremity, reaches its 

 greatest height, 286 feet above mean sea-level and 109 feet 

 above flood-level of the Westfield River, at Mt. Tekoa. From 

 this place it slopes east sixteen feet per mile to the village 

 cemetery, where its height is 232 feet and 87 feet above flood- 

 level of the Westfield River at Westfield. The east end of the 

 Avenue Plain is at least seventeen feet lower than the adjacent 

 ends of the Hampton and Poverty Plains, showing that seven- 

 teen feet of stratified deposits must have been swept off the 

 east end of Avenue Plain. 



When the flood subsided, the overflow from the north ceased, 

 and the Westfield rivers began to flow once more through the 

 Divide Range into the Connecticut By their conjoined action 

 they eroded the Avenue Plain to its present level, and cut for 

 themselves, across the once continuous plain, deep valleys, 

 with the terraced sides that now appear. 



ART. XXX— On some Embryonic Forms of Trilobites from the 

 Primordial Rocks at Troy, 2K T. ; by S. W. Ford. With 

 Plate IV. 



The existence, in the case of a number of species of Bohe- 

 mian Trilobites, of a series of forms showing that, before reach- 

 ing maturity, the animal passed through several widely distinct 

 phases of growth is a fact long ago made familiar to geologists 



