84 L. Lesquereux on the Coal Formations of North America. 
of slow subsidence, the downward movement becoming more 
rapid, the sea broke through its sandy barriers and swept at once 
upon the whole plain, bringing with it the sand of its shores for 
the formation of the sandstone. I do not find this last supposi- 
tion necessary. For, even with a slow movement of subsidence, 
continuous for a while, the sea ought to penetrate to the interior 
of the land, and with its continuous encroachments, bring for- 
ward with it the sand of its shores. This would better explain 
why some strata of coal and sandstone are thicker westward, 
where the bogs grew for a longer time and where the action of | 
the sea was afterwards prolonged. It explains, also, why to the 
westward some veins of coal are double and gene ¥ nore 
' numerous than to the southeastern part of our coal-fields, this 
multiplication being caused by partial retrocession and advance 
of the marine element, which was felt only near the inside of 
the coal-fields and did not reach the deeper outside borders of 
the original basin. But theré is no material difference between 
these explanations. In either case the repeated upheaval of the 
sea-covered land is su ed as a necessary condition of the 
formation of the peat; for this matter can grow only upon land 
where the water of the sea cannot reach. 
To this last assertion which has not been contradicted, we can — 
add the following: that peat never grows on swamps that are 
plained by his remark: that at the time of the inundations al 
* 
from reaching the peat bogs. This damming up was fully bes 
