Maryland Geological Survey 151 



The only explanation I have for (b) is that it is aragonite stained with limonite. The 

 form and undulatory extinction of some of the fragments of this type suggest that they 

 are parts of the shells of some animal — (a) Is probably something similar, but I cannot 

 explain its non-polarizing. The matter requires further study. Most of the flakes of 

 mica and grains of decomposed minerals in this portion are stained green. 



(4) Xon-magnetic 

 Dominant. — Zircon, enstatite, apatite, in about equal amounts. 

 Rare. — Kyanite, rutile. 



( 5 ) Magnetite 

 Almost all in angular grains. Contains, besides, much slightly cloudy, yellowish-green 

 glauconite. Some muscovite and garnet. 



III. Extra Fine Sand 

 General appearance drab olive-green. Light minerals and glauconite in about equal 

 proportions, with of course some rare minerals. The glauconite is both in rounded 

 grains and in irregular fragments. There are some Iimonitic flakes. 



IV. Silt 

 Limonitic flakes are prominent in this portion. There is less glauconite than in the 

 extra fine-grained. 



V. Clay 

 General appearance faint yellowish-gray, with not as much limonitic material as 

 might be expected from the character of the rock. There is a considerable amount of the 

 fibrous material which has been found characteristic of the clays. 



SAMPLES NOS. 7 AND 8 



General Summary and Conclusions. — The significance of sample 8 is 

 largely in its relation to sample 7, so that it must first of all be con- 

 sidered in connection with this. 



In the field the upper part of the marly glauconite sand from which 

 sample 7 is taken was found to be full of pyenodont shells much worn, 

 bored, and sometimes broken. This condition seems to indicate a period 

 of exposure in shallow coastal water. Together with the sharp contact 

 between this bed and the overlying, it proves a disconformity, at least 

 locally. 



The most striking fact about their relations is the almost perfect simi- 

 larity in every respect except the lime content. 



The sands in the upper bed (sample 7, fig. L, p. 169) are a little 

 coarser and a little less perfectly sorted, but in the proportions of sand 

 and clay, the general relation of the different sizes and the mineral content 

 there is remarkable agreement. This extends even to the proportion of 

 glauconite, which is almost exactly the same in the two beds. The only 



