ipO TRANS. ST. LOUIS ACAD. SCIENCE. 



thickness ; this, included with both the iron beds, presents a thick- 

 ness of forty feet. The strike of the formation is N. 50° W., S. 

 50° E. from the true meridian ; dip at the upper cut 21°, and at 

 the lower cut 14°. 



I would here call especial attention to those specimens of iron- 

 ore lying on the table which present a jointed structure ; on the 

 faces of some you will find thin sheets of Calc Spar^ and in several 

 pieces taken from the mass of iron-ore lying in the lower bed will 

 be observed cavities filled with the same mineral. This is a very 

 unusual occurrence, for, though Quartz particularly. Apatite, and 

 other minerals, are frequently found associated with iron-ores, I 

 have never before observed this paragenesis. ' 



The porphyry of Buzzard Mountain comes under the same 

 classification as that back of the Knob from the fact that it is a 

 quartzless porphyry, but its texture is entirely different ; here we 

 have a conglomerate, Miith a dense feldspathic base containing 

 pebbles and fragments of porphyry ; this conglomeratic mass is 

 several hundred feet wide, and is bounded by a porphyry of a 

 dense massive texture ; the conglomerate extends quite across the 

 mountain, and on the south side comes flush up against a dense 

 porphyry which presents a beautiful banded, stratified, and bedded 

 structure. Nearly the same character of rock composes Cedar 

 Hill, with the addition of a jaspery porphyry which is found mas- 

 sive in considerable quantities, and is considered by the miners 

 as an indication of iron-ore deposits. On this hill is a large 

 deposit of Specular and Micaceous iron-ore, in irregular lenticu- 

 lar veins, and irregular masses scattered through the conglomer- 

 atic formation. Portions of the porphyry here dift'er from the 

 previously described porphyries in possessing amygdaloidal struc- 

 ture, in the cavities of which frequently crystals of Orthroclase 

 and Oligoclase are found. 



On Shepherd Mountain there are two varieties, one with a dark 

 matrix containing abundant crystals of quartz ; the other is a 

 porphyry free from quartz, but containing large and abundant 

 crystals of feldspar. (These different varieties you will find here 

 on the table and can examine at your leisure.) Near the summit 

 of the mountain is a dense ffesh-colored porphyry, feldspathic 

 base, matrix containing no crystals, and of a highly conchoidal 

 fracture. This porphyry is very similar to those already described. 

 Interest is added to this porphyry from the fact of its containing 



