750 FARMERS' REGISTER— GREEN SAND AND CALCAREOUS MARL. 



from a greenish yellow to a brown. Besides a 

 considerable proportion of green sand, it contains, 

 in addition to the crystalized gypsum, a notable 

 amount of this substance in a subdivided state, 

 and seemingly occupying the place of the shells 

 which were jbrmerly present, and laave been de- 

 composed under the chemical agency of some 

 substance wliich filtrated in solution through the 

 mass. Incumbent upon this bed is a thin layer of 

 very pure wtiite cki}', of a texture which would 

 recommend it to various useful purposes. Over- 

 lying the clay is a stratum of shell marl in a very 

 subdivided state, containing masses of casts and 

 shells approaching to the hardness of rock. This 

 is the uppermost layer of the eocene or lower ter- 

 tiary formation. Yet in some places a stratum of 

 the ordinary middle tertiary marl rests almost im- 

 mediately upon the former, and would not by an 

 ordinary observer be recognized as distinct. At 

 Coggin's Point, where the succession of strata 

 now noted was observed, a thin and scarcely dis- 

 tinct layer of small brownish red pebbles inter- 

 vened between these two layers of shells, seem- 

 ing to mark a comparatively violent action of the 

 waters in the interval of the two deposites. But 

 an examination of the shells, in these two contigu- 

 ous strata, aflbrds abundant evidence of their 

 belonging to distinct geological epochs. In the 

 upper stratum the large scallops, the common oys- 

 ter of our marl, and all the usual insjredienis of 

 our middle tertiary or miocene formation, may be 

 recognised. In the lower bed lew or none of them 

 exist, but certain characteristic shells belonging to 

 the eocene period are entombed. Similar fossils 

 appear below, in the green sand beneath the gyp- 

 seous earth; and here a great variety of beautiful 

 specimens may be discerned. An enumeration of 

 these fossils in this place would of course be at- 

 tended neither with utility nor interest, and in- 

 deed, were it advisable in "the present stage of the 

 inquiry, it could not be made, on account of the 

 necessity of comparing the specimens whh shells 

 from other localities in Europe and this country, 

 in order to identify species, and to decide upon 

 those which are new, or peculiar to our own for- 

 mation. That many such exist, I have every rea- 

 son to believe, and with future leisure it is hoped 

 that they will be named according to the fashion 

 of the day, and described in the appropriate place. 

 It will however be of real value to the reader, in 

 any inquiries which he may institute, in reference 

 to this ibrmation, to obtain some general idea of 

 the characters of two or three of the more conspic- 

 uous and characteristic shells. The observer will 

 perhaps be able to recognize the follovi^ing: — 



1st. The cardita planicosta. This shell is of 

 various sizes, rarely however equalling that of the 

 clam. In tbrm it bears some resemblance to that 

 Bhell; but on the convex side a number of flattened 

 ridges run li-om the knobbed extremity near the 

 hinge, spreading from each other and enlarging as 

 they approach the margin. The hinge part of the 

 shell is very thick. This shell, occurs abundantly 

 in the eocene or lower tertiary ol' Europe, and al- 

 so in that of Alabama. 



2nd. Ostrea seUtxformis, or saddle-shaped oj's- 

 ter. This shell is very ])eculiar, having, when 

 lull grown, such a lateral extension on each side as 

 to present, when the hollow of the shell is turned 

 down, a verj- distinct resemblance to a saddle with ' 



its two depending f^aps. It is found abundantly in 

 the eocene of Alabama. 



3rd. Fvsus longaevis, a small shell less than 

 an inch in lenglli, and resembling in general form, 

 those Avhich are commonly called conchs. It is 

 however flattened down on one side as if it had 

 been subjected to pressure. This shell occurs abun- 

 dantly in the eocene of Europe^but I believe has 

 not until now been discovered in the corresponding 

 formation of this country. 



These three fossils, which are all found In great 

 nurnbers in such of the eocene localities in Vir- 

 ginia as I have examined, are sufficient to iden- 

 tify the formation wherever they may be discov- 

 ered. But as already indicated, they" are accom- 

 panied by a variety of other shells, a large pro- 

 portion of which, would appear to be peculiar to 

 this particular region. It would seem that the 

 eocene of Virginia though agreeing in most re- 

 spects with that of Alabama, contains some 

 fossils found also in the Paris eocene, and which 

 are absent from that of Alabama. 



In most of the specimens of marl from this re- 

 gion hitherto examined, besides a large amount of 

 green sand, I have found a considerable propor- 

 tion of gypsum, and in some of them as much as 

 forty or fitly per cent, of carbonate of lime. Spe- 

 cimens received from Dr. Corbin Braxton, at 

 the Piping Tree, were found to contain, along with 

 much green sand, a great amount of the carbo- 

 nate of^ lime, and some gypsum. Judging from 

 its composition and texture, it must be looked up- 

 on as a very valuable manure. At Coggin's 

 Point, the lower stratum before described, contains 

 from sixty to seventy per cent, of the green sand, 

 with a small proportion of carbonate of lime, and 

 occasionally a little gypsum. The next deposite 

 above, (the gypseous earth) abounds in gypsum, 

 but contains less green sand than the former. Of 

 this ingredient, however, it still possesses a very 

 considerable proportion. In alluding to the power- 

 ful effects of the gypseous earth, in a trial which 

 he made, the author of the Essay on Calcareous 

 Manures describes them as much greater than 

 could be accounted for by the pro))ortion of gyp- 

 sum present, and hence throws oat the suggestion 

 that some other fertilizing ingredient was contain- 

 ed in the earth. This additional efl'ect must doubt- 

 less be ascribed to the presence of the green 

 sand. 



In prosecuting the geological survey of Ma- 

 ryland, Professor Ducatel has been enabled to ascer- 

 tain the existence of a green sand deposite through- 

 out an important district of that state. Of its ex- 

 istence on both sides of the Potomac I was al- 

 ready fully aware — and it affords me much satis- 

 fiictioii to find that the suggestions based upon 

 general geological considerations, which were 

 presented in my former paper, have already been 

 so actively and ably followed up by this enlighten- 

 ed and diligent observer. Of the identity of some 

 of the green sand deposites described in his report, 

 with that now ascertained to exist in the eocene 

 of Virginia, I am as yet by no means convinced; 

 b'jt a minute geological examination, such as that 

 already inslituted in Maryland, and that which is 

 looked to with some interest in Virginia, cannot 

 f lil to throw ver)^ useful light on this, as well as all 

 the other important deposites in the tide-water 

 region of the two states. Mutual benefit would 

 arise fi-om the co-operation of surveys, conducted 



