60 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Montpelier Beds. 



Homogeneous textured white chalky limestone with flints, peet. 

 resting unconformably upon the Cambridge beds .... +500 



Cambridge Beds. 



Yellow colored granular limestones (blue before oxidation) 



alternating with clays, with many fossils ±100 



Blue, black, and purple clays grading into above ±100 



Richmond Beds. 

 Blue and black clays without calcareous beds grading down 



into thin alternating beds of clay and sandstone ±25 



Purple colored clays, without regular lamination .... ±25 



Slightly calcareous beds in above ±25 



Purple and blue-black arenaceous clays, extending down to 



bed of Great River +200 



The clays and marls are black and unctuous in some places; in others 

 they are yellow, excessively calcareous, and full of minute Foraminifera 

 (Miliolidse), and grade from black into blue and gray colors upon drying, 

 and into yellow on oxidation. The Foraminifera are so abundant that 

 they give an oolitic look to some of the rocks, but on oxidation they 

 crumble into small specks of pulverulent lime. This lime, after solu- 

 tion and redeposition, largely makes the segregations of limestone. 

 Sometimes the clay seams are so bituminous they have the appearance 

 of thin lignitic beds. 



The limestones occur in layers of various thickness up to two feet; 

 they are nodular and irregular both in thickness and texture. At some 

 places they are firmly indurated, at others they are friable and shaly. 

 They are clearly chemical and clastic segregations in the great mass of 

 clays, and gradually increase in proportion as we ascend in the series, 

 while the clays similarly decrease. In freshly exposed portions the 

 limestones are also blue-black in color. On weathering they become 

 bright yellow, as a result of the oxidation of small amounts of iron 

 which accompany the fossil colonies. 



Many fossils — Echinoderms, Corals, Rudistes, and other Mollusca — 

 which are listed in another chapter of tliis report, occur in the cal- 

 careous portions of these beds, both as free shells in the clays or 

 making the greater mass of the limestones. Some of the latter in the 

 cuts south of Catadupa are almost entirely composed of Rudistes, which 

 also occur more sparingly in the beds at Cambridge. Oysters and 



