Lyman.] '^^'" [May 18, 



New Red is compiled from the United States Geological Survey topo- 

 graphical sheets so far as published (some parts of the Connecticut field 

 being deficient), and from Percival's geological map of Connecticut, of 

 1843, and Prof. Emerson's map of the Massachusetts New lied, and 

 Prof. Davis' partial mapping of the Connecticut New Red ; but a number 

 of changes have been made according to the indications of the topography. 

 These geological maps gave, for our present purposes, chiefly the outside 

 limits of the New Red and the occurrences-of trap. The topography 

 seemed to indicate clearly the necessity of reducing the extent of the trap, in 

 some places very much ; and, even as now drawn, the breadth of the trap 

 may be, strictly speaking, somewhat exaggerated, though probably harm- 

 lessly so and not inconveniently for better couspicuousness. Notwith- 

 standing the short-sighted niggardliness of the Connecticut government of 

 the time, that did not enable Percival to give in his report more, he says, 

 than "a hasty outline, written mainly from recollection," of his ample field 

 observations, his map has been the great authority for the Connecticut 

 New Red ; but it is painful to find that the base itself of the map is 

 exti lely inaccurate, not unlike other maps of that date, and even later, 

 in States further west and south. It is probable, also, that he considered 

 every bowlder of trap to indicate that solid trap in place lay immediately 

 below ; and consequently many of his trap masses have no corresponding 

 topographical indications. Prof. Davis has already made some just criti- 

 cism of the map, and, for example, has said : '•' that the little ridges north 

 of Toket inountain, marked with much detail of curvature on Percival's 

 map, are disappointing when examined on the ground" (U. S. Geol. Sur- 

 vey, 7th Ann. Rept., p. 481). It seems highly improlsable but that many 

 of the numerous marks for trap on Percival's map cannot represent trap 

 in place. In Eastern Pennsylvania, quite outside the region of glacial 

 drift, exposures of trap in place are very rare, and it is not easy to sup- 

 pose that they can be anything like so common as his map would seem to 

 indicate in a region heavily covered with drift. It has consequeuily 

 seemed proper enough to omit many of his smaller trap masses from the 

 present map, wherever there was no topographical feature to corroborate 

 their existence. The lack of the New Haven topographical sheet, not yet 

 published, has perhaps led to the omission of some of the little trap 

 masses that might have been inserted, but they would not be important 

 for the present purpose. 



As Prof. Davis has justly remarked, many of Percival's curves in the 

 trap are simply the result of variations in the shape of the surface of the 

 ground, where the outcrop of a bed or sheet, dipping gently, retreats as it 

 sinks into a valley, or advances as it climbs a hill, and such curves may 

 be properly retained. But some of Percival's curves do not seem to have 

 any real support in the topography ; and at other places, for example, 

 north of Middletown, the topography gives quite a changed interpretation 

 for the structure. In Massachusetts, too, near Mt. Toby and at the east- 

 ern end of M^t. Ilolyoke the topography seems to require the changes that 

 have been made in the mapping of the trap. 



