John Magens Mello

“ As rock-crystal, the typical form of quartz, is an hexagonal prism terminated at each end by a rhombohedron, when broken it will be seen to have a conchoidal or splintery fracture. Rock-crystal is very widely distributed, being found in rocks of all ages. The most beautiful and perfect specimens are usually obtained from large cavities or geodes in the older igneous rocks, and also from veins in these and other rocks. The size and color of quartz-crystals vary greatly; some are so small as to be microscopical, while others are of very considerable bulk. ”

“ A bed of lighter earth (No. 3) succeeded the red bed, and was present everywhere in the cave, varying in thickness from 1 foot to 2 feet. The usual bones and teeth of the Pleistocene Mammalia, including the Bear, Wolf, Woolly Rhinoceros, and Reindeer, were found in the cave-earth. In one place, 6 inches below the stalagmitic crust, a ramus of the lower jaw of the Hyæna, with its condyle and coronoid process intact, occurred: and near to it, under a large block of stone, were found part of the lower jaw of Cervus megaceros and a fine quartzite flake ”

“ Orthoclase Feldspar.⁠Fig. 3.—Plagioclase Feldspar.
shown us what granite is made of; but we are now beginning to learn that, would we know something of the real history of a rock, a far minuter examination is needful, and geologists are rapidly learning that they must turn to the microscope if they would receive answers to many important questions, both as to the history and also as to the composition of rocks. A marvelous light has been shed during the past few years on rock-structure through this minute investigation, especially with the aid of polarized light. ”

“ At about 120 feet from the door a small fissure was found opening out of Chamber A to the right, below the original level of the floor. As in the case of the fissure at the extremity of Chamber F in the Robin-Hood Cave, this was filled with red sand nearly but not quite in contact with the roof. The surface of the sand was also dry and powdery, and it was destitute of fossil contents. The digging has not been carried on beyond this point in Chamber A, the few remaining feet giving little promise of having any thing of sufficient value to repay the work of exploration. ”

“ THE study of rock-structure is one of great interest to the geologist, and not only does it teach him the various materials of which any particular rock is built up, but it will often lead him to the knowledge of wonderful facts relating to its origin and past history, and will enable him to trace some of the many changes to which it may have been subjected during the lapse of time. ”

“ The three principal agencies that have taken part in the formation of quartz are heat, water, and organic life. When we examine, by the aid of the microscope, certain forms of quartz, such, for instance, as the crystals occurring in some of the quartz porphyries, and occasionally in the pitchstones, as well as much of the quartz of granite rocks, we find that they contain minute cavities which inclose very frequently tiny crystals of other minerals ”

“ Great care has been taken to keep the contents of the different beds separate, each bed having been worked out, as far as possible, independently, and the earth riddled as it was removed to the mouth of the cave ”

“ We know that quartz requires a higher temperature to melt it than does either the feldspar or the mica, and so, had the granite been formed as are regular volcanic rocks in the ordinary way of igneous fusion, we should certainly have found that the quartz would have crystallized before either the feldspar or the mica, and it would have been seen in definite crystalline form, and its crystals would have interfered with and penetrated those of the other mineral constituents of the rock. ”

“ In this no remains of any sort were found.
8. Chamber C.—It will be observed that comparatively few bones were discovered in Chamber C, large as is this portion of the cave. The rock floor in it was generally nearer to the roof than in the other chambers, and the deposits of cave-earth and sand were, on the whole, less thick; at the extreme left a considerable stalagmitic deposit is to be seen coating the rock. The comparative absence of bones in this chamber may perhaps be attributed to the presence of a stream of water running for some time through this branch of the cavern. ”

“ It has been noticed as somewhat remarkable that the quartz in granite should have been usually the last mineral to crystallize, although it is that one which is the most difficult to fuse, and which would therefore naturally be expected to have been solidified before the feldspar and the mica. But it has been shown that, when quartz is in combination with other mineral substances, it is often as readily fusible as they are ”

“ It will hardly be necessary to do more by way of recapitulation than just allude to the first papers read, which have established the fact that we have at Creswell a series of highly important caves, illustrating by their contents two periods of human occupation during the Palæolithic age in Britain, when man was contemporary in Derbyshire and the adjoining district with the characteristic Pleistocene fauna. ”

“ Carnelians and sardes are only color distinctions of chalcedony; and the immense family of agates, including the onyx and sardonyx, is more or less composed of chalcedony, disposed in layers, regular or irregular, and combined with other forms of quartz, such as amethyst, jasper, etc. This latter name is applied to an aluminous variety of quartz: it is opaque, and has a less crystalline appearance than ordinary quartz. It is very varied in color: some beautiful red, brown, and green-banded stones are obtained in Siberia, in Egypt, and elsewhere. ”

“ The few remains found in the breccia consisted, as before, of bones of the Hare, a few teeth of the larger Pleistocene Mammalia (R. tichorhinus, Hyæna, Bear, and Horse) , together with fragmentary flint implements and a small piece of ruddle.
4. The Cave-Earth.—The succeeding deposit, that of cave-earth (3) , was very uniformly distributed throughout the cavern, although varying very considerably in thickness in different parts. Near to the entrance, as has been observed in a previous paper, it was very thin where the breccia attained its greatest development ”

“ In a similar manner mica is another mineral which may be a source of supply for pure silica. A fact of some importance in studying the mode of the formation of quartz is that, unlike feldspar and other minerals, which in crystallizing pass at once from the fluid to the solid state, quartz passes through an intermediate viscous or colloid condition before it assumes the crystalline form. ”

“ Amongst these bones there were also a perfect ulna of a bear, and several milk-teeth of the Mammoth, besides one large fourth molar which Mr. Heath was fortunate enough to find near the old wall: this measured 11 inches in length by 9 inches in height.
1. The Talus.—When we resumed work this year we began, as we had done at the Robin-Hood Cave, by making an examination of the talus at its mouth (fig. 10) . ”

“ In a large group of agates, of which beautiful specimens come from India, an appearance of banded formation is seen, which, upon microscopic examination, resolves itself into an infinite number of red or brown spots, regularly arranged in bands or concentric groups: these spots appear to be segregations of oxide of iron. ”

“ Now, when we begin to examine a piece of one of these granites, we see at once that it is not an homogeneous stone—such, for instance, as is a bit of flint but that it is built up of various dissimilar-looking materials ”

“ The value of this discovery, the first of its kind made in this country, need scarcely be insisted upon. But we have yet to record another discovery of as great, if not greater, importance. At the far end of Chamber F, in the same cave-earth, at a depth of about 1 foot, Prof. Dawkins had the good fortune to see extracted, by a workman, a canine of Machairodus latidens, an animal whose remains, as all will be aware, have only twice before been found in England—the Rev. ”