4:04c -C. Schuchert — Paleozoic Crustal Instability 



and the Acadian Mountains of New Brunswick and Nova 

 Scotia. And when we proceed from Kansas to southern 

 Oklahoma, or from Missouri to central Arkansas, and note 

 that the Pennsylvanian formations of from 1000 to 3000 

 feet thickness swell out to 10,000 and even to considerably 

 more than 18,000 feet locally, we are again justified in 

 postulating mountains to the southeast in Llano (Fig. 6), 

 the roots of which are in all probability now buried under 

 the deposits laid down later by the Gulf of Mexico marine 

 invasions of Cretaceous and Cenozoic time. These two 

 examples are both marine fossil deltas, and they are a 

 striking attestation of orogenic work, indicating moun- 

 tains whose presence and geographic position are postu- 

 lated from the migrated, fragmented mountains now seen 

 in the marine formations mentioned. There are in addi- 

 tion many other such cases of marine sedimentation, 

 though of less striking record. 



We see therefore that great piles of marine deposits 

 are indicative of mountains and of crustal deformations. 

 In all similar cases of marine sedimentation, it is very 

 probable that the regions of orogenies lie more or less 

 far away from the places of clastic accumulation. In the 

 case of thick masses of fresh-water or continental deposi- 

 tion, on the other hand, the record of orogeny is far better, 

 for these depositions take place in, or at least near, the 

 areas of the mountains themselves. One such example — 

 and it is a brilliant one — will be cited in some detail 

 because it brings out clearly a succession of orogenies, in 

 fact, four of them, all taking place during Mississippian 

 and Pennsylvanian times. This is in the region of New 

 Brunswick and Nova Scotia, in the Acadian province (see 

 Fig. 6), in the area now being studied by Dr. Walter A. 

 Bell of the Geological Survey of Canada, who kindly pre- 

 sented me with the following facts. Succeeding the late 

 Devonian orogeny already referred to, were developed the 

 Lower Horton arkoses and agglomerates, and the Albert 

 series of New Brunswick, which together have a thickness 

 of up to 3400 feet. The fossils seemingly indicate very 

 early Mississippian time, and this conclusion is further 

 borne out by the underlying and overlying formations. 

 Then followed the first Carboniferous crustal movement, 

 apparently not as vigorous a one by far as that of the 

 Devonian. Again we have basal arkoses, in the Upper 

 Horton E stheria-hearmg beds of more than 700 feet thick- 

 ness, and then about 1100 feet of Windsor semi-marine 



