Report on the New York State Museum, 47 



The marl is composed of the dead shells of fresh water mol- 

 lusca and of carbonate of lime which lias probably been carried 

 down in solution from the Eelderberg limestones and deposited 

 in the valley. A short distance south of the locality under con- 

 sideration and in the same valley is another deposit of the same 

 character but somewhat larger. A smaller deposit lies about a 

 mile to the northwest. There are other deposits, at various 

 places in Greene county. They occur in hollows in which a con- 

 siderable basin must be filled up before water can drain off. 



The exact thickness of the deposits of muck and marl is not 

 known. The muck is probably about four to five feet thick in 

 some parts. An iron rod betw.een ten and eleven feet in length 

 was thrust perpendicularly into the bed by the writer. As only 

 slight exertion was necessary to push the entire length of the rod 

 in, it is probable that the deposit of marl is more than seven feet 

 in thickness — how much more it is impossible at present to say. 



Calcareous tufa is not found in considerable quantities. Small 

 scales of it have formed on the rocks about one of the holes into 

 which the water in the northern lot drains. These scales are 

 one-quarter of an inch thick and are composed of several thin 

 layers. 



The marl contains only aquatic species of mollusca. The 

 following is a list of the species that have been collected: 



Valvata tricarinata, Say. 



Yalvata sincera, Say. 



Planorbis campanulatus, Say. 



Planorbis trivolvis, Say. 



Planorbis bicarinatus, Say. 



Planorbis exacutus, Say. 



Planorbis parvus, Say. 



Limnaea humilis, Say. 



Carychium exiguum, Say. 



Physa heterostropha, Say. 



Physa ancillaria, Say. 



Bulinus hypnorum, Linn. 



Sphserium rhomboideum, Say. 



Spha?rium SpJ (young of a rhomboid species). 



Pisidium Virginicum, Say. 



Pisidium ventricosum, Prime. 



