NORTH AMERICAN GEOLOGY. 199 



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

 «h'i)osi(e(l npoM 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 surveys have been in progress for some time, and interesting 

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

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

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

 Southern States. 



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

 for the general mouoclinal structure of the Trias, especially of the 

 east-dipping beds of the Connecticut Valley. 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 and across it at a small 

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

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

 mand that, when 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 : 



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

 east to west, it may be supposed that one of the easiest ways of yield- 

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

 inclination should steepen and their horizontal 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, and 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 one 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 neighbors by faults with upthrow on the 

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

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

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

 perfoi-ce follows the deformation of its foundation, and thereby acquires 

 a faulted mouoclinal attitude. The explanation of the Triassic mouo- 

 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 in great 

 part on the changes in the surface shape of the greater deeper mass 

 below.* 



The principal evidence in favor of this hypothesis is the occurrence 

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

 rocks which strike across the Triassic areas at a small angh\ These 



* Americaa Assoc. Proc, vol. 35, pp. '2-24-227; Am. Jour. Sci., ii, vol. 32, pp. 342-352. 



