July 14, 1916] 



SCIENCE 



57 



mite molds. In either case the calcitic shells 

 evidently were deposited in a dolomite ooze. 



(5) Perfect dolomite rhombs are sometimes 

 embedded in compact, horn-like calcitic beds. 



(6) Dolomitization bears no relation to the 

 present pore space of beds as it probably 

 would if it had been affected by underground 

 waters. 



That replacement was an important process 

 in dolomitization is shown by the bunchy dis- 

 tribution of dolomite in mixed beds of dolo- 

 mite and limestone, by the invasion of cal- 

 citic fossil casts by dolomite rhombs, and by 

 local dolomitization adjacent to or within 

 pervious marine structures, worm borings, 

 shell cavities, etc. Dolomite grains in contact 

 with calcite were all rhombohedral, but had no 

 calcite inclusions. Anhedral form was the rule 

 for dolomite grains in contact with their own 

 kind. Certain facts suggest that dolomitiza- 

 tion may take place by direct precipitation 

 near the sea bottom, and by recrystallization of 

 magnesia-bearing skeletons. Proof for the 

 latter processes was not obtained. 



Fossils and the shallow water structures of 

 most dolomites show that, like most limestones, 

 they were laid down in shallow warm seas. 

 Salinity seems to have favored dolomitization, 

 since dolomites are common in the enclosed 

 basin deposits. Chemical and mineralogical 

 studies show that dolomites contain isomorph- 

 ously combined ferrous oxide. This shows 

 positively that dolomites were laid down under 

 reducing conditions. 



The writer was able to differentiate calcite 

 from dolomite very successfully with a modi- 

 fied form of the Lemberg solution consisting of 

 4 grams of fresh AlCls crystals, 6 grams ex- 

 tract of logwood, 1,400 grams of water, boiled 

 for 20 minutes with constant stirring and then 

 filtered. Dolomite turns blue in a dilute solu- 

 tion of HC1 about 1/10 normal with a few 

 drops of freshly prepared potassium ferricya- 

 nide because of its ferrous iron content. 

 Sedimentary calcite in all cases did not show 

 a trace of ferrous iron. 



Edward Steidtmann 



Geological Department, 

 University op Wisconsin 



CELLOIDIN PARAFFIN METHOD 



Many of the difficulties encountered in sec- 

 tioning hard and brittle objects (chitin, eggs 

 with yolk, etc.) may be overcome by the use of 

 a method which I find is not generally known 

 or used in this country, and which I have been 

 asked to publish in Scoince. It is the celloidin- 

 parafiin method of Apathy, 1 published by him 

 in detail in 1912. Although long, this method 

 combines the advantageous qualities of both 

 the paraffin and celloidin methods, without in- 

 troducing any disadvantages of either of these 

 methods. There is no shrinkage as in the cool- 

 ing of paraffin; ribbons can be cut and spread 

 out on the slide by warming as with paraffin; 

 thin sections may be cut even in warm weather, 

 due to the firm nature of the infiltrated cel- 

 loidin. The method consists of embedding the 

 object in celloidin, clearing and dehydrating 

 the hardened celloidin block, and then in- 

 filtrating with paraffin the celloidin block with 

 its contained object. The chief advantage of 

 Apathy's technique lies in the use of his oil 

 mixture, which is given below. 



The method is as follows: 



1. Fix, wash and dehydrate material in the 

 usual way, finally putting through three 

 changes of absolute alcohol. 



2. Put into a tube of ether-alcohol at least 

 5 hours, keeping the object high in the tube. 

 (Test tubes of various widths serve nicely for 

 this, the object being held wherever desired by 

 a loose plug of dry cotton wool inserted in the 

 liquid.) 



3. Two per cent, celloidin for twenty-four 

 hours, deep in the tube. 



4. Four per cent, celloidin for twenty-four 

 hours, deep in the tube. 



5. Put object into paper embedding box (or 

 small dish) of four per cent, celloidin, and 

 harden in chloroform vapor twelve hours. 



6. Quickly trim excessive celloidin from the 

 object, leaving a few millimeters on each side, 

 and put deep into tube of chloroform for 12 

 hours. 



7. Put into a tube of Apathy's oil mixture 



i Apathy, S., 1912, "Neuere Beitraege zur 

 Schneideteehnik, " Zeitschr. wiss. Mikr., Bd. 

 XXIX., S. 449-515, 4 textfiguren. 



