Regarding the 'FREQUENCY OF THE METEORITICAL EVENTS OF MEGATONIC CLASS' I decided to put the dates into a visual format to get a better idea of their frequency. Here it is:

One can clearly see that the frequency of events increased towards 1935.
Using 'meteoritic events since 1930' as a search term, some interesting material popped up:
The Day The Earth Trembled by John McFarland, a page from the Armagh Observatory, has an account of the 13 August 1930 Brazil event, with information that is different from that quoted by Vitaly Adushkin & Ivan Nemchinov.
Here is a pdf document entitled 'Brazilian Impact Craters': _http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1546.pdf
At this url: _http://www.xtec.es/recursos/astronom/craters/amazonase.htm is an article entitled: 'Two "Tunguskas" in South America in the 1930's?' Originally printed in IMO's December 1995 edition of the WGN Journal. It was written by Duncan Steel of the Anglo-Australian Observatory, with references.
From the last mentioned page, the following is the wording of a Newspaper article printed in The Daily Herald on March 6, 1931:
+ MENACE OF METEORS LIKE HUGE BOMBS FROM SPACE
+ HURRICANE OF FLAME
+ BLAZING BOLTS FIRE FORESTS
+ MANKIND'S LUCK
Another colossal bombardment of the earth from outerspace has just been revealed.
Three great meteors, falling in Brazil, fired and depopulated hundreds of miles of jungle.
News of this catastrophe has only now reached civilization because the meteors fell in the remote S. American wilderness.
It was yet another lucky escape of mankind from an appalling and unrealized peril.
The last great meteor fell in Siberia in 1908. In a district so remote that only last year were details of it's destruction given to the world. Had either of these two meteor falls chanced to strike a city in a densely populated country, frightful loss of life and damage would have been cuased. "A Meteor", Mr. C.J.P. Cave an ex-president of the Royal meteorological Society stated recently "carries in front of it a mass of compressed and incandescent air.
When it strikes the earth, this air "splashes" in a hurricane of fire...The Brazilian meteors are reported (says the Central News) by Father Fidello of Aviano. writing from San Paulo de Alivencia in the state of Amazonas, to the papal newspaper, "Osservatore Romano".
BLAZING FOREST The meteors fell almost simultaneously during an amazing storm. Terrific heat was engendered. Immediately they struck the ground the whole forest was ablaze.
The fire continued uninterrupted for some months, depopulating a large area. The fall of the meteor was preceded by remarkable atmospheric disturbances. At 8 o'clock in the morning the sun became blood-red and a penumbra spread all over the sky, producing the effect of a solar eclipse. Then an immense cloud of reddish powder filled the air and it looked as if the whole world was going to blaze up.
WHISTLING SOUND The powder was succeeded by fine cinders which covered trees and vegetation with a blanket of white. There followed a whistling sound that pierced the air with car-breaking intensity, then another and another.
Three great explosions were heard and the earth trembled. The Siberian meteor of 1908 completely destroyed the forest over an area of 70 miles in diameter. It's roar was heard 600 miles away and it's glare maintained twilight all night even in England.
Reading the article I was struck by this:
The fire continued uninterrupted for some months, depopulating a large area.
Which reminded me of this:
A: Well, the burning fragmentary shower ignited much of the land areas in what you now refer to as Western Europe. This had the results you can imagine, causing the resulting societal breakdown you now refer to as "The Dark Ages."
I can understand how a fire continues uninterrupted for months in the Brazilian rain forest. The heat dries out the trees and the ground and renders everything inflammable. But how did the burning fragmentary shower ignite much of the land areas in what you now refer to as Western Europe? Maybe the land was more heavily forested at that time? Do comets/meteors release some inflammable substance when they explode which adheres to anything with which it comes into contact, and burns slowly?