The rocks of this region are shales and limestones, with 

 sandy layers in the upper portion of the exposed series. The 

 shales predominate, and commonly split into thin laminae or 

 lenticular pieces, which lie essentially parallel to the bedding 

 plane. These shales weather into clayey soil by the solution 

 of the carbonate of lime, which here commonly forms an 

 important cementing constituent. In this clayey soil we 

 find a return to the more primitive condition of the material, 

 for these slates were beds of clay before they assumed their 

 present consolidated character. This clay, which was spread 

 out over what was formerly the ocean floor, was derived 

 from the disintegration of the rocks which formed the 

 land at that period of the earth's history, rocks which were 

 constantly attacked by the waves on the shore, the rivers 

 and streams along certain lines on the surface of the land, 

 and the atmosphere, wherever they were exposed. When the 

 streams had brought their load of debris into the sea, where 

 the waves and shore currents could distribute it, an assort- 

 ment took place, the coarsest material being deposited near 

 shore and the finer farther out to sea, in direct proportion to 

 the degree of its fineness, and the strength of the current. 

 It was only the clay — the result of the chemical decomposi- 

 tion of the rocks, and the finest rock flour — the result of the 

 most effective comminution of the rocks, which -were carried 

 out into the comparatively quiet water at a distance from 

 shore, and there deposited to form beds of mud. The empty 

 shells of dead animals, which were strewn over the bottom 

 of the sea in this region, as well as many still occupied by 

 the animals, were buried in this accumulating mud, just as 

 empty shells are buried on the modern beach, and as living 

 mussels are buried more or less deeply in the fine material 

 deposited off shore. The fine mud gradually found its way 

 between the valves and filled the space once occupied by the 

 soft parts, a condition characteristic of the occurrence of most 

 bivalve shells on modern mud-flats. When in the course of 

 time the mud became a shale, the shells became incorporated 



