Will you always find shells? The dirt changes from brown to black then deep red then sandstone The red dirt does not produce much at all.But nice items do come out of it and it is very hard to dig by hand and stays together in clumps it wont sift. How does the seasoned digger handle this situation. We think we also found a fire hearth in the red stuff the upper section we only found some snapped bases in there. Guess they were mad and just chucked the shafts into the fire.Anyone have something to share.
P.S.
We have never found any shells

No, you won't always find shells. The other kinds of shells not yet mentioned here are a now extinct species of snail shell, of which were extremely high in protien, and sea shells brought in from the gulf coast (far less frequent). I've seen snail shell layers with no soil 10 to 12 inches thick in middens along walnut creek (East Austin) before those sites became dug out in the 70's. As for the red clay problem, I have had some experience similar to what you described at a site along the colorado river in fayette county. The site wasn't far up the bank from the river, and had a red clay paleo and transitional paleo layer in it. It was real frustrating trying to dig it with a pick and avoid breaking a nice point.
The land owner observing our delima suggested using his track loader on it. Well, we wern't sure what to think about that, and reluctantly agreed. After all, he was the land owner, it was free for us, and we'd see the result first hand. So, he dug up several cubic yards of red clay and put into seperate bucket piles. When he was done, he climbed down of the machine and with a surly grin said.....well boys....come back in about a week! We did, and to our amazement, the clay had dried out almost completely and it would immediately crumble, and was even easily for sifting! We had a hay day and all the piles were gone through in a single day. Alot of good stuff was found, and to our further amazement, we did not see any freshly broken points from the use of the tractor!
Not an easy or affordable solution for most, but in this situation, it did work well!

In continuation of the above, we dug a site in Northwest Austin in the 60's where a large rock slab protruded out of the midden top. We envisioned the indians sitting on it making nice points. We steaked off a 12 foot square with the slab in the middle. We dug it out to original ground level in about 2 weeks at an average depth of 3 feet. We did find a few whole points, but not nearly as many as hoped for. One one side of the slab, we found mostly broken bases. One the other side we found mostly broken tips. We wound up matching and glueing back together 3 times more points than the whole ones found (all middle and late archaic). Thus, we were left to believe that they intentionally broke many pieces probably to prevent any potential rivals from re-using them. I have alw3ays found more broken points that whole when digging into hearths, or fire boxes as we used to call them.