THE RELATIONS OF GEOLOGY TO AGRICULTURE. 549 



and mica schist, which, by the action of the air, rain, and frost, readily 

 decompose, and the lime and other fertile ingredients are leached out 

 and diffused through the soil, where the roots of the growing crops can 

 readily assimilate them. In consequence of this ready decomposition of 

 the ledges, every small stream has excavated very much material ; and 

 this region is full of steep hills, often conical. These steep hillsides 

 are fertile, as may be instanced in the towns of Cornish and Lyme. 



Furthermore, there are considerations tending to show that the adja- 

 cent granite hills are benefited by the proximity of the limestones. The 

 study of theoretical geology seems of little practical importance to many 

 people ; but, by examining scratches upon ledges, and other phenomena 

 on the surface, we can say positively that immense masses of ice once 

 travelled over the state in a general southerly direction (but varying 

 greatly in different portions of the state). This ice, in its onward prog- 

 ress, broke off fragments of the ledges, and distributed them over the 

 country. Hence, as the granite region lay in the path of this mighty 

 stream, blocks of limestone came over its surface, and, by their de- 

 composition, have tended to improve the soil. These may be found 

 throughout the western border of the gneissic region from Dixville to 

 Hinsdale. 



Another benefit comes from the presence of the calcareous rocks. By 

 their decomposition, numerous small molluscous animals are enabled to 

 obtain the material for their shells. They consequently abound in calca- 

 reous countries, since they here find one of the essentials to their exist- 

 ence in great abundance. The aquatic tribes of mollusks exist in such 

 great numbers that their remains accumulate at the bottom of ponds in 

 deposits several feet thick. More than thirty of these beds are described 

 in the geology of Vermont, in the region just spoken of. I have seen as 

 yet only two in New Hampshire, one in Columbia, and the other in 

 Brookline. The lime is nearly pure, and can be burned for quick-lime, 

 or spread upon the land fresh from the swamp. The pond-way has dis- 

 appeared by filling up, and remains only as a swamp. The importance 

 of these marl beds makes it desirable for those living upon the calca- 

 reous regions to search further. It would give me great pleasure to visit 

 any deposit of this kind that may be discovered by the farmers within 

 our state limits. The farmers will understand that lime and plaster are 



