178 



SCIENCE. 



[Vol. XXII. No. 556 



places along Eock Eiver, and exposed in many railroad 

 cuts. While the general exposure is only of the yellow 

 or buff stone, in several localities ,it has been quarried 

 down to the blue. With a piece of each color in hand, 

 and the quarry itself under close insisection, a valuable 

 series of facts may be discovered by the pujDils — the 

 strata joints, seams, etc., whether they are equally distinct 

 in all parts of the exposure, whether adjoining strata are 

 decided contrasts; if so, in what respects, color, texture, 

 homogeneity, hardness, etc. Enquire which strata are 

 the oldest, and why so decided '? Which strata are best 

 adapted to the purpose of quarrying ? As a building 

 stone, will it be greatly aif ected by water ? Weigh a 

 fragment in its natural condition; dry it as fully as pos- 

 sible and weigh again, — a druggist's scales will give the 

 change. Judging from various exposures, does the 

 stone "weather" smooth or in depressions ? Can you tell 

 the original upper surface of a flagging stone from the 

 lower? How? In building, is it better to "lay" the 

 stone with any reference to this original surface ? Why ? 

 With a hand magnifier of ordinary power, examine the 

 texture of the rock, coarse or fine? Are there occasional 

 little "pockets" in it ? Is the sand in these the same as 

 in the rock itself ? Those white, irregular stones, imbed- 

 ded here and there, what are they, and how do they differ 

 from the others ? They are flint or quartz, — strike them 

 sharply with a piece of steel, — fire flies. What are those 

 little brick-red masses here and there ? How do they 

 differ in texture and shapie of grains ? Is the rock firmer 

 or less firm in their vicinity ? They are iron nodules. 

 Are they beneficial ? Why ? Note the reddish powder 

 around any nodule, if kept damp, and how the stone 

 streaks. What other forms have you found ? An incrus- 

 tation ? Yes. Touvertine, a deposit of carbonate of lime 

 from the water trickling among the strata. How do you 

 know it is a carbonate ? This time try nitric acid instead 

 of hydrochloric on these peculiar forms, carbonate, quartz 

 and iron, — note the difference of action. In this way a 

 thousand things familiar to every geologist will be 

 learned by the student, and bring to him the inspiration 

 of a discovery. 



The pupils have gathered all the fossils they could, 

 whether many or few. Some are manifestly corals and a 

 form allied, fossil sponges; others are shells. Separate 

 them. What do they suggest as to the origin of the 

 rocks ? Wliere were they formed ? Are they more closely 

 allied to salt or fresh water species? Examine carefully 

 the valves, hinge line, ribs or striae, beak and umbo, sinus 

 and folds. Find specimens giving both internal and ex- 

 ternal structures or characteristics, if you can. Distin- 

 guish between a cast and the fossil itself. Are the casts 

 of any value ? What ? Classify, as well as may be, all 

 the fossils collected, according to form, and according to 

 internal structure, so far as it can be traced. Not all shells 

 that look similar on the outside belong to the same 

 genus, nor do all belonging to the same genus look alike, 

 necessarily. After the student has made a goodly collec- 

 tion of fossils and facts about them, the teacher may lead 

 him on, with State Reports and other authorities, till the 

 final identification is reached, but the pupil should take 

 every step himself for himself, when able. . In all these 

 lectures and quizzes, the blackboard is an invaluable help, 

 making diagrams as you progress, rather than present a 

 more perfect one, completed before the class enters. 



At Eockford, also, we have a fair exposure of the Drift. 

 After studying the stratified rocks as such, the class is 

 ready to study stratification as presented here, and to 

 make further maps or diagrams. Note the sizes of the 

 gravel stones and their arrangement. Is there a regular- 

 ity in distribution as to size of pebbles? Few better 

 fields in a prairie section can be found for the varied 



forms of quartz. Occasionally bits of mineral are found, 

 — galena and copper, — the former suggesting the mining 

 districts of Northern Illinois and Southern Wisconsin; 

 the latter, from its form, the Lake Superior region. Fos- 

 sils of various kinds are not infrequent, but of genera 

 and sp)ecies quite different, usually, from those found in 

 the quarries and railroad cuts. The drift has brought 

 them from several formations and from long distances. 

 Oftenthe internal and external structures of these speci- 

 mens are better preserved than in those imbedded in the 

 rock. Indeed, most of the best and most exact descrip- 

 tions of palaeozoic corals have been based upon drift 

 specimens. The pupil's having made collections of the 

 different varieties of rock from the drift, the teacher may 

 here give some ready tests of identification for common 

 forms, or some simple mineralogical table. We have few 

 bowlders, but those few, with the drift rocks, submit them- 

 selves to the same kind of study as rocks in situ, whether 

 macroscopic, microscopic, or chemical, so are well adapted 

 to all petrographic study, save geographical limits. 



At Eockford we have the deep, heavy prairie deposit, 

 black as are all rich soils due to the decay of vegetable 

 substances. If this soil is burned, there is little change, 

 save in color, — the mass is argillaceous matter, with a 

 little fine sand. The stratification noticed in the walls of 

 wells, and in artesian well borings suggests the same 

 agency as the quarry and the drift, viz. : water; but the 

 occasional shell fragments found bear little resemblance 

 to those in the quarry, rather to our fresh-water Unio, 

 Anadonta and Paludina, genera still living in the rivers 

 and marshes. The inference, then, is that at some remote 

 time, but later than the quarry and the drift with their 

 salt-water fauna, there was a fresh-water lake, perhaps 

 an arm of Lake Michigan, reaching out toward the Missis- 

 sippi Eiver, or the Mississippi extended this way. 



As the conservation of energy has given us a new 

 physics, so the microscopic study of rocks and fossils has 

 given us a new geology. Though microscopic rock-sec- 

 tions were first made in 1854, it was not until they were 

 introduced into Germany a few years ago, that they be- 

 came an active agent in geologic research. Only by this 

 careful method can these petrified thoughts of the Cre- 

 ator be fully understood. Palaeontology is essentiallybio- 

 logical, dealing with the plants and animals on the globe 

 rather than with the life of the globe, but it has rendered 

 an inestimable service in determining the question of 

 evolution, so the microscopic section will be of inestimable 

 service to the petrographer with his crystalline rocks, 

 whether volcanic, plutonic or metamorphic. For' making 

 these sections let the pupils use their own ingenuity in 

 preparing the simple ajjparatus really essential. If a sec- 

 tion cutter is at hand of approved pattern, or an electric 

 or foot-power lathe, very well; but if not, it is just as well, 

 for with cold chisel, hammer and file, the student can 

 easily reduce his specimen to a proper size for grinding. 

 The superficial surface may be as large as p)referred, but 

 the thickness not more than one-fourth inch, if the intention 

 is to make a translucent slide. If only one surface is to be 

 ground, the only care will be to get the angle desired for 

 the examination. . For early work only calcareous speci- 

 mens should be used. Let the student furnish himself 

 with a plate 12x16 inches of floor glass, smooth on one 

 or both sides; a half-dozen pieces of double or treble thick 

 glass 2x2 inches, a half-dozen spring clothes pins, emery of 

 4-7 grades, the finest being emery "slime;" a piece of 

 chamois skin, stretched tightly over a smooth board to 

 polish upon; some Canada balsam, hard and soft; some 

 alcohol, a lamp and some matches, and a little water. 

 With a few needles in wooden handles, and a firm table 

 to work upon, he is independent of surroundings. His 

 patience, time and skill will be taxed, but these are the 



