Hi everyone: great topic sure generating alot of interest and information.

As I read all the posts I truly believe that no one answer is correct for any one situation or area of North america.

One has to realize that technology did not travel fast in those years, the old millwrights resisted change the same as today in many areas of our society.

I rtemeber quite well growing up in Ontario Canada, where tractors and horses for quite anumber of years operated side by side, usually until a new generation came along or strict regulations created an immediate need for change.

From what I have found out in my research was that circular saws were invented in England around 1800 that corresponds quite well with the information above.

What was a big factor was the power required to drive them and keep them up to a minimum operating speed under load. Large water turbines of upwards of 40 to 50 hp were in operation and could drive them but was not always available in a country setting, at least here in (most) of rural Ontario.

Along came the portable Steam engine which created the power supply in the country setting, now all that was needed was a person with the money and drive to put this all to work.

Around my area in the 1867 census one steam powered saw mill was in operation. With this information, and the fact that hundreds of single blade mills were still in operation in the same area and would continue to cut for many more years, made dating historic structures alittle easier.

Remember that muley mills or sash mills could cut no longer than 20 foot logs this governed by the length of the saw frames, and the length of the sawmill building itself. The blade was usually installed in the centre of the sawmill meaning that the whole log if it was 20 feet in legth would rest on a saw frame of about 24 feet beginning its journey by the blade. It also had to travel completely by the blade so it needed at least 24 feet on the opposite side.

In our mill the saw frame would actually advance through an opening in the wall for a short distance to complete the cut, and be suspended in open air.

It was this period that sawn, hewn, and circular sawn lumber could be present in the same structure, around here that could have happened after 1867, but not before.

Long top plates continued to be hewn until late 1800's (around here), and then gradually the long hewn plates gave away to short timbers scarfed together.

Sort of confusing to many readers I am sure NH