1886.] 



MICEOSCOPICAL JOURNAL. 



115 



Richmond Diatom Deposits. — 

 In a review of W. B. Rogers's Ge- 

 ology of the Virginias published in 

 the Amer. Jotirn. Science, we find 

 the following paragraph relating to 

 the discovery of the infusorial de- 

 posit : — . 



• A second point relates to the his- 

 tory of the first discovery of the 

 famous infusoi'ial bed^ which crops 

 out conspicuously along the slopes 

 of the hills on which the city of 

 Richmond stands, and at several 

 other places in Virginia, as well as 

 on the Maryland side of the Potomac. 

 Although this interesting feature of 

 our geology has for years commanded 

 the attention and admiration of the 

 scientific world, and the beautiful 

 picture of its diatoms developed bv 

 Ehrenberg's microscope, become 

 familiar to the eye of every geologist, 

 we doubt whether manv of our 

 younger co-workers know much 

 about the history of its first discovery. 

 We deem it proper, therefore, to sav 

 that, after giving a general account 

 of his first discovery and microscopic 

 examination of the contents of this 

 wonderful deposit of what was then 

 regarded as " infusorial animals," 

 Rogers says, " In view of these in- 

 teresting facts, the discovery of the 

 infiisory Stratum, as one of the 

 members of our series of Tertiarv 

 deposits, cannot fail to be regarded 

 as an important edition to our knowl- 

 edge of the Tertiary of this country, 

 and has the greater interest at present, 

 as being the first example vet ob- 

 served in the United States of the 

 occurrence of infusorial remains in 

 any byt the most recent geol(;gical 

 formations." His latest view of the 

 geological positic^n of this formation 

 is, that it is near the base but still 

 within the Miocene gi7)up. We arc 

 ready, from personal observations, to 

 accept this conclusion.' 

 o 



Microscopic Writing. — At a 

 recent meeting of the Microscopic 

 Section of the Literary and Philo- 

 sophic vSociety of Manchester, Mr. 



Alfred Brothers, F. R. A. S., read 

 a note on microscopic writing, in 

 which he said : — ' The Lord's Prayer 

 has alwavs been a favorite subject for 

 testing the powers of minute calig- 

 raphy. To write the 227 letters 

 within the space covered by the 

 smallest coin is a feat of some difii- 

 cvilty, but that the same number of 

 letters can be engi-aved on glass with- 

 in a space so minute as to be almost 

 invisible with the lowest powder of 

 the microscope, and the individvial 

 letters not defined clearly with an 

 eighth object-glass, ma}' seem incred- 

 ible. There is. however, in the pos- 

 session of this Section a slide which 

 contains the Lord's Prayer, written 

 by W. Webb in 1S63, within the 

 space of the 40^,oooth part of an 

 inch. To find this minute speck re- 

 quires the exercise of much patience, 

 as it is not only necessary to have 

 just the right kind of illumination, 

 but the focus of the lens must be on 

 the true surface of the glass on which 

 the object is written. When once 

 seen with a low power it is not diffi- 

 cult to find with the same power ; 

 but with the half-inch and higher 

 powers it is always a trial of patience 

 even when the position of the object 

 has been carefully registered with a 

 lower power, and you are sure that 

 the object is central in the field. 

 Perhaps with the achromatic con- 

 denser some of the difficulty inay be 

 removed. It will be remembered 

 that about twenty years ago the late 

 Mr. Rideout presented to the Section 

 a machine for producing minute 

 writing. The instrument was lent 

 by Mr. Rideout to Mr. Dancer, by 

 whom it was recently sent to the So- 

 ciety. It seemed to me that as this 

 instrument was purchased by Mr. 

 Rideout at the Great Exhibition in 

 1862, it might be the same with which 

 the wonderful piece of writing, or 

 perhaps it should be called engrav- 

 ing, referred to, was executed. I 

 therefore wrote to Mr. Dancer for 

 information on this point. In reph' 

 he says : *'The microscopic writing 



