48G SULPIIUUET OF IRON IN GYPSEOUS EARTH. 



distant. But omitting such merely speculative matters, there are 

 practicable and profitable operations to be based on the knowledge 

 of the succession and dip of the strata. Thus, when the existence 

 of rich marl is known in any point, and its depth, it is almost cer- 

 tain that it will thin out towards the north-west, and cither thicken, 

 or maintain its then thickness, as proceeding south-eastward, On 

 land north-westward of the disappearance (at top) of a rich bed, 

 (as 4), and however near, it would be in vain to search for the like. 

 The boring for any practicable depth on most of the river land of 

 Marlbourne '(for example) could reach only the poor beds exposed 

 at the surface for some ten miles, including the beds marked 3 and 

 2, perhaps, also. But on land south-eastward, and near to the 

 surface exposure of any rich marl, it might be expected to reach 

 the like at some greater depth. The lowest eocene marl which I 

 reached by sinking the pit for examination 25 feet below tide on 

 Evergreen (described p. 462), and which must have been near to 

 the bottom of the lowest bed, exhibited the same peculiar appear- 

 ance, and some of the peculiar fossils, which are also to be seen in 

 (M) the lowest of the Pamunkey layers, and at an exposure thirty 

 miles distant. In no other localities had I seen either the same 

 appearance of marl, or the same rare shells, as some of both common 

 to these places only. In the much deeper pit sunk for examina- 

 tion on Coggins Point (p. 465), though the rising of water at 49 

 feet prevented deeper digging, the fossils then reached indicated 

 the near approach to the same lowest marl found at less depth at 

 Evergreen, and exposed much above the river at North and South 

 Wales. Hence, it may be inferred that this lowest and very pe- 

 culiar bed of this great formation, as well as the formation generally, 

 is continuous under all this broad surface of territory. 



Many specimens of the marl and gypseous earth of the Pamun- 

 key beds, were made partially red hot, for the purpose of showing 

 whether sulphureous fumes were so disengaged, as was stated on a 

 foregoing page (460) to be the case with most specimens tried of 

 the James river gypseous earth. This result was obtained in all 

 of sundry trials of the gypseous earth (3) below the marl (4) in 

 the marl at South Wales (M), and in some cases, but not generally, 

 of the richer marl 4. In the still higher and poorer marl (5), 

 which I lately have excavated extensively in the Clifton bank, the 

 sulphureous fumes were obtained in every trial. A specimen of 

 marl from Pipingtree, and many specimens of the gypseous earth 

 (upper part of 3) from Newcastle ferry, Newcastle farm, and from 

 Marlbourne, all gave out these fumes. Sundry other specimens of 

 calcareous green-sand marl which were thus treated, yielded no 

 fumes. The latter results were found in specimens from the several 

 diggings at Newcastle (both sides of the river), and at Mr. (I. W. 

 Bassett's bank, Farmington. It may not be useless to repeat here, 



