"The vicinity of Huashen Town and Qingliang Mountain are this kind of soil." When I was a child, I lived in my grandmother's house for a while, every rainy day, the road was muddy, no matter what shoes I worn, there would be a lot of mud stuck to the shoes, and the more sticky the more sticky, only with a stick to remove the mud, can I continue to walk." Guo Lao said as he pinched a little soil with the thumb and index finger of his right hand, and then twisted it, "Director Feng, you see, this kind of soil is indeed very sticky, when building a wall, you only need to use this kind of soil, it is precisely because this kind of soil is relatively clayey that all can be attached to the gap of this city wall brick for a long time, because of the strong viscosity, the closure of the soil is relatively strong, and the outside silt cannot penetrate into the brick joint." ”

The author mentioned this Huashen Town earlier, and its location is in the southwest of Liuyedu, two or three miles away from the scene of the crime.

"Director Ma led us to Huashen Town, and many people in Huashen Town have this kind of city wall bricks." Li Wenhua said, his meaning is very clear: many homes have city wall bricks, and it is not easy to find the traces of the murderer.

"Guo Lao, along the Qinhuai River, where else is this kind of clay?"

"I only know that Huashen Town and Qingliang Mountain are this kind of soil, I haven't studied this problem specifically, other places, we can investigate, this shouldn't be a difficult thing." Guo Lao Dao.

"Old Guo, how do you know that Huashen Town and Qingliang Mountain are of this kind of clay?" Yan Jianhua asked.

"My grandmother's house is near Huashen Town, near the river, and as for Qingliang Mountain, we once investigated a case in Qingliang Mountain, and it was a rainy day, and the road was very muddy, so I was very impressed."

Therefore, Ouyang Ping decided to conduct a field investigation on the soil on both sides of the Qinhuai River tomorrow.

At eight o'clock in the morning of October 29, a patrol boat stopped on the river in front of Zhonghuamen Castle, and at eight o'clock, two cars parked outside the south gate of Zhonghuamen Castle, and Ouyang Ping and his party of ten people walked down from the car. In addition to the six comrades of the criminal investigation and Guo Lao and Ma Minglong, there are also two fresh faces, one is a soil expert specially invited by Director Feng, the old expert's name is Ji Queqi, a professor at Jingnan Agricultural University, and the other is Professor Ji's assistant, his name is Hu Qiwei, and he is about 35 years old.

The patrol boat went all the way to the west.

The comrades spent a whole day traveling from Zhonghuamen Castle to the Three Forks River (the confluence of the Qinhuai River and the Yangtze River).

The content of this expedition is the soil along the Qinhuai River.

There are four places along the Qinhuai River with the same soil quality as the clay in the cracks of the bricks of the city wall, one is Huashen Town and the surrounding area, the second place is Qingliang Mountain and the west side of Qingliang Mountain - the west of Huju North Road to the Qinhuai River, and the third place is the area directly opposite the crime scene and the area near the Ma Po Nunnery, which was a small hill before the temple was built. The fourth place is between Moling Road and Liuyedu. The soil in these four places is exactly the same as the soil of the loess deep in the brick gaps of the city wall. The person who came to this conclusion was Professor Ji.

So, Ouyang Ping decided to investigate these four places. According to Guo Lao's opinion, while investigating the four places, he continued to investigate the boats on both sides of the river as planned, looking for traces of the deceased.