Hello Thomas, I am actually a Gerhardt cousin of yours, and have researched many of my German ancestors, some are related to you, but even the ones that aren't share a common history.
On the other side of my family I have many that came from Strembeni, Kishinev, Bessarabia, Russia. That is a small town near the Romanian Border west of Odessa.These ones also came from Galicia, Austria, although they referred to it as just Austria.
Now here is the possible interesting connection with the Markewitz name.Your grandmother, Mary Busch's (nee Gerhardt) parents and grandparents came from the Volynian German area in Russia or Ukraine.Her grandparents were named Jakob Gerhardt and Maria- Anna Wagner and in the St. Petersburg archives they are listed as having several children in this area in the 1870's and 80's. You can find that at, http://www.odessa3.org/collections/stpete/volhynia/http://www.odessa3.org/collections/stpete/volhynia/ Unfortunately the record for our our ancestor, Charles or Karl Gerhardt (1870 or 71) is not included. BUT of the children that are included they are all born in the Zhitomir PArish and in each case the name of the town is mispelled, but one can tell that they were trying to spell the same name and I think it could be similar to Markewitz. They include Milnitzu, Mitnitza?, Mitnija, Michnitz?, and Metschalka. They are phontecally very similar, and so many factors go into figuring these names out. First there is the person recording it and then there is the person interpreting it over 100 years later, there's different accents, dialects and languages. I also supsect that the abillity to read, write and spell that is taken for granted today played a role in the recording of these names back then.
So maybe the Gerhardt and Busch connection followed a similar path in Europe.I also know other other German Russians in my other family tree branches that started in "Austria" went to Bessarabia, arrived in Grenfell, Sask and then to St. Boswells. There name was Dorwart and I don't think there is any left in that area anymore. They eventually gravitated towards Weyburn area.
If you have any questions ask away.
Oh one other thing the commuity history book fro Grenfell called, Grit and Growth -has information on the Ortt family that is related to you Leonhart.I would have to check - Phillip ORtt might be a brother to your Katharine - I would have to check.