365 



in a smooth, almost unbrokeu bed, for the distance of forty rods, form- 

 ing a f utidaliou to the dam above, and disappearing in deep water be- 

 low the mills. The rock is of duik gray color, occasionally porou?. A 

 specimen contained hornstone. 



Rock was also occasionally found forming the bed of the channel 

 from Flat Rock till wiihin two miles of Ml Pleasant, and large tabular 

 masses but little worn, appeared even farther up, proving the existence 

 of rock in place at no great dist;ince. 



A very slight general dip in the limerock of this county, north-west- 

 erly, is observable. 



MARL. 



The only deposits of shell marl known to exist in this cor.nty in suf- 

 ficient quantity for economical purposes, are in the town of Plymouth. 

 The followincr dei^erve notice : 



Od section 22 (at Deacon Purdy's,) is a small deposit which occupies 

 two-thirds of an acre. As other beds occur in the township of similar 

 origin, it may be advisable to notice the circumstances of its formation. 

 Upon a gentle slope a protuberant bog has formed, which is wet and 

 slightly tremulous. It consits of peat, or vegetable matter, having a 

 depth of about 3 feet. Below this is found the marl, which has here a 

 thickness of from one to three ft-et. It is a plastic substance of a milky 

 gray color, perforated by roots, and may be cut out in masses like clay. 

 The presence of lime is indicated at the surface by a calcareous deposit 

 upon moss. 



Beds thus formed originate chiefly in deposition from water of springs 

 highly charged with lime; circumstances under which tufa, or indura- 

 ted deposits of lime, usually occur. Lime is favorable to the formation 

 of shells, which are generally associated in abundance, but do not con- 

 stitute the bed as when it occupies the former bottom of a lake. Sev- 

 eral species of the genus Helix (snails) are most numerous, with Lym- 

 nea, Planorbis, <fec. 



As the producing causes are still in operation, marl existing under 

 these circumstances may be supposed still in progress of formation. 



Eight hundred bushels of lime have been manufactured at this bed; 

 mufh of it beautifully white and of good quality. 



The marl furnishins: this number of bushels was taken from an area 



