NORTH AMERICAN GEOLOGY. 199 



which it is stated that the peuiusula does not consist of a sand bank 

 deposited upon a coral reef, but of Tertiary and more recent strata con- 

 tinuous with these formations farther north and west. 



MESOZOIC OF THE EASTERN UNITED STATES. 



Trias. — Many of the important questions connected with this familiar 

 formation still remain unanswered, but over most of its area several 

 systematic surv^eyshave been in progress for some time, and interesting 

 results may be expected from Davis's investigations in the Connecticut 

 valley, Dartou's detailed study of the New Jersey and New York dis- 

 trict, and Russell's researches on the liichmond coal field and in the 

 Southern States. 



33. During the past year Davis has proposed a hypothesis to account 

 for the general monoclinal structure of the Trias, especiallj^ of the 

 east-dipping beds of the Connecticut Yalley. He finds in this district 

 that the formation is traversed by numerous faults, mostly with the up- 

 throw on the eastern side and parallel to the belts of crystalline rocks 

 which form the Trias basin, and strike under aud across it at a small 

 angle. The Triassic rocks were originally deposited on the smoothed- 

 off' upturned edges of these crystalline rocks, and the hypotheses de- 

 mand that, wheu the latter yielded to a deep-seated horizontal pressure, 

 the bottom of the basin was deformed and the formation faulted. The 

 mechanism of this process is explained as follows : 



Wheu the whole mass was crushed, so as to diminish its measure from 

 east to west, it may be supposed that one of the easiest wa^'s of yield- 

 ing to the crush was by a little slipping of slab on slab, whereby their 

 incliuation should steepen and their horizoutal measure decrease. If 

 the crushing were more severe near the surface than at great depths, 

 a shearing force would be introduced, that might, if necessary, throw 

 the slabs over past the vertical, aud thus produce reversed dips. As 

 slab slips on slab, the formerly horizontal beveled surface of every one 

 is canted over, so as to dip in oue direction at an angle equal to the 

 change of the inclination of the slabs ', and the surface of every slab is 

 separated from that of its neiglibors by faults with upthrow ou the 

 side of the direction of dip. The Triassic cover is not strong enough 

 to bridge across from ridge to ridge of the uueven surface thus pro- 

 duced ; its weight is much greater thau its strength can bear, and it 

 perforce follows the deformatiou of its foundation, and thereby acquires 

 a faulted monoclinal attitude. The explanation of the Triassic mono- 

 clinal may therefore be included in the following general statement. 

 Wherever unconformable masses are deformed together, the structure 

 given to the lesser relatively superficial mass must depend iu great 

 part ou the changes iu the surface shape of the greater deeper ma,ss 

 below.* 



The principal evidence in favor of this hypothesis is the occurrence 

 of the observed faults and their parallidism with the belts of crystalline 

 rocks w^hich strike across the Triassic areas at a small angl,\ These 



* Amencau Assoc. Proc, vol. 35, pp. 224-227 ; Am. Jour. Sci., ii, vol. 32, pp. 342-352. 



