GOOD EFFECTS OF MARL.--In a conversation with Hugh Maxwell, Esq., some short time since, he stated some facts in relation to the fertilising power of a red marl abundantly existing at Nyack, which induced me to visit the spot. I found Mr. Maxwell's farm of 110 acres bounded by the Hudson, well worth a visit. The whole was in excellent fence, made of the loose stones found on the land, neatly piled about 41/2 feet high, forming fields of from 4 to 8 acres. The formation of these fences has used nearly all the stones which were on the surface of the lands. And in this it would seem as if Divine Providence had caused the rocks to be distributed of the proper size for fencing. Had the pieces been much larger or smaller they would not have answered the purpose so well as they now do. If they had been planted two feet under ground, or had been piled in larger masses, the labor of fencing would have been very greatly increased. This farm, as well as all those about Nyack, lies on the singular mass of sandstone included by a front of about five miles on the river. All the surrounding rocks are of other materials. This sandstone, when quarried, exhibits strata of a kind of red marl of many feet in thickness, lying between strata of the sandstone. The quarry-men throw it out of their way, and millions of loads are lying near the water's edge, so that in many places vessels can lie alongside a bed of it, and slide it on board. On Mr. Maxwell's farm, the former proprietor, desirous of making extensive hard walks through his garden, caused this marl to be put upon them about one foot deep. Soon after this was finished, the walks began to produce clover; the white in such profusion and persevering succession, that all prospect of using the paths in that condition was abandoned: they could not be kept in order by the hoe. Mr. Maxwell being strongly impressed by this occurrence, determined on applying it to the surface of his farm. I saw a field of corn of several acres which had been top-dressed this year with the red marl, now bearing not less than 80 bushels of shelled corn to the acre--as great a product as is obtained from the best city manure, costing at Nyack nearly 37 cents per load. I saw an upland field of wheat, on which, as an experiment, Mr. Maxwell had top-dressed with this marl a space of three rods by two, from which I pulled an average bunch of straw-stubble, that is more than double the size and weight of any like parcel of stubble, to be found in the whole field of several acres. Unfortunately the husbandman had cradled all the wheat indiscriminately, which prevented Mr. Maxwell from examining the separate product of the wheat. I should not hesitate to pronounce it a double product. Mr. M. top-dressed a field of oats with this marl, and the yield was 70 bushels per acre. He top-dressed a field of clover with it the third year from the seeding, and the product is heavier than the crop of the _second year_. This field was dressed with ten