120 Scientific Geology. 



species of pine, occur in peat, several feet below the surface, in the 

 marshes of Charles river. 



Marl 



In limestone regions, the waters generally contain more or less of 

 the carbonate of lime in solution j and this, gradually depositing 

 along with the fine clay or mud held in suspension, produces one of 

 the varieties of marl. In a few places in Berkshire County, such 

 marl is now in the course of formation at the bottoms of ponds. In 

 this marl (No. 12 of specimens)* occur one or two species of Plan- 

 orbis, one of Physa and a Cyclas ; corresponding with existing spe- 

 cies in the same region. 



Alluvium of Disintegration. 



Very few rocks have the power of completely resisting the 

 united influence of air, water, heat and cold. And some kinds are 

 powerfully and deeply acted upon by these agents. Perhaps the new 

 red sandstone is more affected in this manner than any other rock in 

 Massachusetts : and not unfrequently its surface for several feet in 

 depth, is converted into mere sand and gravel. This becomes gradu- 

 ally mixed with the soil, and gives a decidedly red hue to extensive 

 tracts. Next to this sandstone and I am not sure but even more 

 subject to decay is our gneiss ; especially that in Worcester county. 

 Hence in that part of the State hilly as it is we sometimes scarcely 

 see a rock in place, in crossing a whole township. In an excavation 

 which I lately noticed in Spencer, I had an opportunity of observ- 

 ing that a disintegration had taken place in the gneiss, from 6 to 1 

 feet in depth. I could distinguish the materials resulting from disin- 

 tegration, from the diluvium lying above them, by observing that in 

 the former the masses of gneiss, remaining undecayed, had a position 

 parallel to that of the layers of the solid gneiss beneath, being consid- 

 erably inclined ; whereas the fragments in the diluvium exhibited no 

 such parrallelism. I have never seen a disintegration so deep as this 

 in the new red sandstone. Some varieties of trap rock, particularly 

 one on Connecticut river, whose base is wacke-like, and some of 

 the sienites in the eastern part of the State that abound in iron, disin- 



* In all cases where numbers are included in parenthesis in the subsequent part 

 of this report, they refer to the specimens of rocks and minerals which I have de- 

 posited in the hands of Government. 



