Of course, they could have mailed bricks -- which was common before the Post Office banned the practice.
You have always, within the package mailing weight limits of the time, and continue to be able to mail bricks; they are not banned. Even these bricks were mailed, beginning in 1916, but these bricks were the main reason a mailing weight limit was placed on how much one mailer could mail to one addressee within certain specified time periods, such as per day:
In 1916, a 50 pound package of bricks cost 54 cents to mail 125 crow-fly miles which happened to be the distance from Salt Lake City to Vernal. By express company, the same shipment was over 1.5 cents per pound or more than 75 cents each package for that trip. The post office at the time contracted with local express companies to carry mail and that contract price was 1.5 cents per pound for that trip. Those 125 crow-fly miles took 400 road miles to cover the distance.
During 1916, before a 200 pound per day limit of mail from one sender to one addressee was implemented approximately 11-24-1916, 37.5 tons of bricks were mailed to Vernal with each of the 15,000 bricks individually wrapped in paper with 10 brick per crate to meet the 50lb maximum package weight.
Bricks to Vernal were not the only large shipment. 9720 cans of tomatoes were packed in cases and mailed, the twelve tons of cases arrive in one train car load in September 1916.
Here is the Post Office's side of the story:https://about.usps.com/who-we-are/p...f-vernal.pdf
Not covered in the pdf was another change which circumstances such as the Salt Lake City to Vernal created. Parcel Post Zone distances were set up on the basis of crow-fly or straight line distance. Zone one was to 50 miles average and zone 2 from 50 to 150 miles average. However the new rule stated that if the actual mail route distance exceeded 150 mile then zone 3 (over 150-300 miles average) rates were to be charged. Thus the fifty pound zone one or two package would not be 54 cents, it would be rated at $1.14.