Friday, May 20, 2011

Test Pit #6

So, I actually wrote this post a few weeks ago but wasn't able to actually post it until now so think of it as a flash back to when we weren't digging excavation units.

On 4/16/11 my group consisting of Kristen, Promise, and I dug test pit #6 on the bottom of the hill. It was situated on the transect of 10m-20m on the East Bering line and on 40m on the North Bering line. It was near a yellow flag but I do not know what the yellow flag was marking. We were digging a 50cm x 50cm pit but we were unable to dig that deep. The top layer of dirt was very hard and dry. It was difficult to break ground even when standing on the shovel. There were cracks in the ground which helped with the digging but then resulted in huge dirt clumps that we had to break with our trowels and the shovel. From 10-20cmd the ground was a little bit softer and moister with dirt clumps. From 20-30cmd the dirt was very soft and powdery when it wasn't in clumps. Most of what we found was in the 0-10cmd level and we found less things the deeper we went. The main things of what we found was a nail, a hook/bent nail (not sure which), and some charcoal. Overall, it wasn't very promising which is probably why all our excavation units were placed at the top of the hill. It was nice to finally dig though and to not have to do surface survey or use the transit compass, neither of which are my favorite things to do in class.

A Trip Down Macadam Lane

Figure 1: Asphalt paths in a Southern California cemetery circa 1920. Note the surface layer of asphalt is crowned over a foundation layer of sub-grade material.

Following up on the Trench 1 discussion. The possible macadam road coming to light is of interest for a couple of reasons: a.) it provides a date range, and b.) it is an unusual feature not often seen or discussed in historical archaeology.

Tar Macadam Pavements

A tar macadam road consists of a basic macadam road with a tar-bound surface. It appears that the first tar macadam pavement was placed outside of Nottingham (Lincoln Road) in 1848 (Hubbard, 1910; Collins and Hart, 1936). At that time, such pavements were considered suitable only for light traffic (i.e., not for urban streets). Coal tar, the binder, had been available in the U.K. from about 1800 as a residue from coal-gas lighting. Possibly this was one of the earlier efforts to recycle waste materials into a pavement!

Soon after the Nottingham project, tar macadam projects were built in Paris (1854) and Knoxville, Tennessee (1866) (Hubbard, 1910). In 1871 Washington, D.C. extensively used a "tar concrete" for road construction. Sulfuric acid was used as a hardening agent and various materials such as sawdust, ashes, etc. were used in the mixture (Hubbard, 1910). Over a seven-year period, 156 acres (630,000 square meters) were placed. In part, due to lack of attention in specifying the tar, most of these streets failed within a few years of construction. This resulted in tar being discredited, thereby boosting the asphalt industry (Hubbard, 1910). However, some of these tar-bound surface courses in Washington, D.C., survived substantially longer - about 30 years. For these mixes, the tar binder constituted about 6 percent by weight of the total mix (air voids of about 17 percent). Further, the aggregate was crushed with about 20 percent passing the 2.00 mm (No. 10) sieve. The wearing course was about 2 inches (50 mm) thick. Hot tar paving products have not been used in the U.S. for many years. (source: Pavement Interactive)

There is a voluminous amount of engineering technical literature discussing macadam road systems and, after spending much of the week perusing the various incarnations such roads could take, this particular variant deserves mention:

Double Pitch Grouted Macadam. Road Board Specification No.4, to Be Laid and Consolidated in Two Layers. – Section 4. The finished thickness of this section will be 4 ½ inches. The material used for the lower layer will consist of broken-up calcerous sandstone (Kentish ragstone), graded from 3 ins. Down to 2 in. gage. The lower layer is consolodiated by rolling , and the pitch binder, the same as in Section 3, is poured in but not brought up to the surface of the stones forming the lower layer, the pitch lying ½ in. below such surface with the object of providing a key for the upper layer.

For the upper layer will be composed of hornfels or elvan from the Penlee (Cornwall), broken to 1 ½ -in gage, costing 12s. per ton delivered on the road with 5 per cent of chippings of the same stone graded from ½-in. down to ¼ -in., costing 7s. 6d. per ton delivered on the road to be added during the process of final rolling so as to form the finished surface. The quantity of pitch required for the double grouting for the two layers is approximately 3 to 3 ½ gals. Per yard super.
The surface is to be finished by the chippings added during the rolling as in the case of single pitch grouting. The Kent County Council will construct this section. (Source: Engineering & contracting, Devoted to the Economics of Civil Engineering Design and to Methods and Costs of Construction, Volume 36, July-December,(Myron C. Clark Publishing Company, 1911), p. 228)

About eleven years later, the construction standards are materially the same; however, there is distinction made between heavy and light trafficked roads:
The thickness of the pitch-grouted macadam coat is is usually 2 in. on lightly trafficed road, and from 2 ½ to 3 in. on other for single pitch-grouting, and from 4 to 4 ½ in. for double pitch-grouting.

The material for pitch-grouting is broken to 1 ½ in. standard gage. In addition to this, 10 per cent of chippings of the same stone, varying from 3/8 to ¾ in . is used for closing after grouting with the melted pitch. The pitch employed usually complies with Roads Department specifications as follow, the viscosity being modified to suit climatic and local conditions by varying the quantity of tar oils. (Source: Engineering News Record,Vol. 89, July 1st-December 31st, (McGraw-Hill Company: New YorK, 1922) p. 565)

In the late 19th and early 20th century, a wide variety of road systems were developed and patented. Among them were systems utilizing bituminous binding agents for rock aggregates. Figure 1 above discusses some possible interpretations of DSCQHR T1 feature.

The possible DSCQHR macadam lane appears composed of a two layer construction similar to the double pitch-grouted macadam specifications. There appears to be a foundation layer(Red A) and a macadam road surface (red B). The foundation layer appears constituted of consolidated calcerous sandstone of which a fair amount has been recovered at the site (see image below).

The macadam layer appears to contain a considerable amount of hornfels aggregate.

Given the slope of the surrounding topography, the DSQHR macadam lane may have incorporated terracotta drainage tiles at regular intervals to handle wet season sheet-wash (see red C).

Given that we have the engineering specifications for construction thicknesses and material size standards, it is possible to determine if the DSCQHR feature fits such an identification.

Lastly, it is possible to assign a general date range between 1877 and the early 1920s for construction of this particular feature.

As a historical aside, tar macadam and asphalt paving systems were favored near schools on the premise that such pavements were more quiet and therefore less disturbing to students. Here is an excerpt from the San Francisco Call to this effect:

Want Noiseless Pavement in Front of Schoolhouse – Supervisors Order Asphalt to Be Laid on Harrison Street Between Fourth and Fifth.

The Supervisors’ Street Committee yesterday reported in favor of paving with asphalt the roadway of Harrison street between Fourth and Fifth. The Board of Works had recommended that the block be paved with basalt blocks, excepting the portion thereof in front of the Whittier School, which was to be paved with either asphalt or bitumen, the entire work to cost $13,500. The committee decided that the entire block should have a noiseless pavement for the good of the school. (San Francisco Call, Volume 98, Number 64, 3 August 1905)

How marvelously considerate!

Trench Level 2

Last Saturday (May 14th) we started the second level of the trench only to find out that we may have mis-measured during the first week. Oops! The problem is that its really difficult to level the line from the SW to the SE corner because of the slope of the hill and the distance of (5meters) and the short nails. So basically, to get the line high enough on the lower lever then the nail would be out of the ground and unsecured. So what to do? What to do?

The only option at the time is to measure the second level at 10-20 cm at the best of our ability and keep on truckin'. First thing next week though, I am bringing some supplies to fix the problem and we will double check to make sure that we measured the depth correctly.

Besides that though, we were able to extract some pretty amazing things. We uncovered still more bones, large pieces as well as an almost complete vertebrae. I am hoping that in the next level we will be able to uncover additional large bones that might help indicate what animal it was. Pictures to come soon!

Breaking Ground

May 7th we started on the trench at the east end of the site. This was really exciting for me as I have not excavated a trench yet and it was a completely new experience that I couldn't wait to start. By mid morning my crew had located what we thought was the best possible location to start the trench according to some of the surface artifacts that had been located the previous week. We chose a spot in which one of the very few pieces of obsidian has been found so we were hoping to find a number worked pieces below the surface.

The 5x1 trench was started with a point at the SW corner. To find the NW point, we measured 1 meter 30degrees West of North and then staked out the remaining SE and NE corners. There was some difficulty leveling the line due to the slope of the trench but we made due.

It was time to break ground! We were able to complete the first level (0-10cm) and dry screen everything before the end of the day. I was thrilled to find once small piece of worked obsidian along with other things such as seashells, a bead, ceramic and porcelain shards, glass, mortar, modified rocks, nails, screws, brick and a large amount of bone fragments (non-human).

It will be interesting to see what we find in the next level as I am sure that there are more bones to come.

Thursday, May 19, 2011

Dig Day 6: May 14th

Last Saturday was our second day excavating units. By some chance of luck, I got to work in the 5x1 trench again! The Saturday before (5/7) we found a lot of possible artifacts, and I was excited to return to the same unit. It definitely is challenging to work with such a large space, but with so many hands, it went fairly smoothly. Amber led our crew- which consisted of Dani, Yanna, Melissa, Mark, Vanessa, David, and myself.

Our unit seemed to hold up pretty well from last week. Our tarp still covered the unit, and all the rocks/ logs were in place. Last week we had some difficulty mainting the unit’s wall integrity, but nothing too serious. A couple times some of the walls crumbled a little bit. When we removed the tarp, there was a little dirt that had crumbled down, but only in a few spots. There was no signs of disturbance from animals or insects that I saw. The soil was hard, slightly moist (which later turned a bit clay-like as we dug), and was filled with rocks.. Our unit measured 5m by 1m.

The first thing we did was catalogue our artifacts from last week’s excavation (level 1: 0-10cm.) We counted and described dozens of possible artifacts including fragments of bone, tile, ceramic, porcelain, charcoal, burnt rocks, glass, and a bead.

Afterwards Vanessa and I moved to the wet screening with another two crew members, while two more used a dry screen and the final two crew members dug. Last week we quickly noticed that the diggers were able to fill the buckets much quicker than the screeners could empty them. Still, it was challenging to keep up the pace. The water screen really helped speed up the process. It was very satisfying to see the clay-like dirt drip away so quickly. However, I definitely need to wear rain boots next week! Vanessa and I found in our screen pieces of concrete, porcelain, pottery, bone, glass, tile, brick, nails, and a bead. Most of our crew used a ¼ inch screen, but I think at one point some used an 1/8 inch screen.

After lunch, I moved over to dry screening and some digging. Our crew found several really interesting items in the 10-20cm level. Yanna uncovered a cement square block that had a mortise on two sides. Each side was 7-7 and ½ cm long. Our crew also found in the first part of the day an extremely large nail/ spike.

We also found the largest piece of tile I have seen yet. It was about 12.5 cm long, 2cm thick, and had a visible curve.

Later, Yanna also uncovered something interesting. Unsure of what it was (and mostly just because I wanted to use my paintbrush) we brushed away the dirt. It looked like a large piece of concrete. David suggested later that it might be part of a path to the well house. Later, we uncovered another large fragment of concrete.

I created a table describing the locations of these objects. I also *attempted* to draw a diagram marking these items’ locations. It is to scale, but I have never done this before, so I may have done some things incorrectly.






Nail/ Spike

A large rusted metal nail or spike, slightly bent

In 10-20cm level



Roof Tile

2cm thick, orange, slight curve


From 90– 99cm (artifact covers 9cm)

From 407- 419.5cm

Cement Block

2cm mortise on two sides, each side is 7- 7 ½ square

In 10- 20cm level



Piece of Concrete #1

Large, imbedded in a deeper level

In 10-20cm level

25.5- 41 cm

478- 498 cm

Piece of Concrete #2

Medium sized piece of concrete, completely in level 2 (10- 20cm)

15.5 cm

19- 32 cm

401- 412 cm

Here are some other smaller finds from the day: ceramic, porcelain, nails, brick, tiles, glass, and bone.

Mammal Vertebrae: